ODERN 


SIR  JOHN  LUBBOCK 


THE 


OAR 


H.MARSHALLWARD 


This  book  is  DUE  on  the  last  date  stamped  below 


!«flf  8-1197! 


flfeofcern  Science  Series 

EDITED  BY  SIR  JOHN  LUBBOCK,   BART.,  M.P. 


THE    OAK 


MODERN    SCIENCE    SERIES. 

Edited  by  Sir  JOHN  LUBBOCK,  Bart.,  M.  P. 


L  The  Cause  of  an  Ice  Age. 

By  Sir  ROBERT  BALL,  LL.  D.,  F.  R.  S. 

H.  The  Horse: 

A  Study  in  Natural  History. 
By   WILLIAM    HENRY    FLOWER,    C.  B., 
Director  of    the  British    Natural 
History  Museum. 

in.  The  Oak: 

A   Popular    Introduction   to   Forest 

Botany. 
By  H.  MARSHALL  WARD,  F.  R.  S. 

In  press : 

IV.  The  Laws  and  Properties  of  Mat- 
ter. 

By  R.  T.  GLAZEBROOK,  F.  R.  S.,  Fellow 
of  Trinity  College,  Cambridge. 


New  York  :  D.  APPLETON  &  Co.,  1,  3,  &  5  Bond  St. 


Plate  L 


THE  OAK  IN  SUMMER. 


THE    OAK 


A  POPULAR  INTRODUCTION   TO 
FOREST-BOTANY 


BY 

H.  MARSHALL  WARD 

M.  A.,    F.  E.  S.,    F.  L.  S. 

LATE  FELLOW  OF  CHRIST'S  COLLEGE,   CAMBRIDGE, 

PROFESSOR  OF  BOTANY  AT  THE    (IOYAL  INDIAN   ENGINEERING  COLLEGE, 
COOPER'S  HILL 


NEW  YORK 
D.   APPLETON   AND    COMPANY 

1892 


COPYBIGUT,  1892, 

BT  D.  APPLETON  AND  COMPANY. 


All  riglits  reserved. 


0  / 


EDITOE'S  INTRODUCTION. 


THE  works  to  be  comprised  in  this  Series  are  in- 
tended to  give  on  each  subject  the  information  which  an 
intelligent  layman  might  wish  to  possess.  They  are  not 
primarily  intended  for  the  young,  nor  for  the  specialist, 
though  even  to  him  they  will  doubtless  be  often  useful 
in  supplying  references,  or  suggesting  lines  of  research. 

Each  book  will  be  complete  in  itself,  care,  however, 
being  taken  that  while  the  books  do  not  overlap,  they 
supplement  each  other;  and  while  scientific  in  treat- 
ment, they  will  be,  as  far  as  possible,  presented  in 
simple  language,  divested  of  needless  technicalities. 

The  rapid  progress  of  science  has  made  it  more  and 
more  difficult,  and  renders  it  now  quite  impossible,  to 
master  the  works  which  appear,  almost  daily,  on  various 
branches  of  science,  or  to  keep  up  with  the  proceedings 
of  our  numerous  Scientific  Societies. 

A  distinguished  statesman  has  recently  expressed 
the  opinion,  that  we  cannot  expect  in  the  next  fifty 
years  any  advance  in  science  at  all  comparable  to  that  of 
the  last  half -century.  Without  wishing  to  dogmatise,  I 


vi  EDITOR'S  INTRODUCTION". 

should  be  disposed  to  hope  that  in  the  future  the  prog- 
ress of  science  will  be  even  more  rapid. 

In  the  first  place,  the  number  of  students  is  far 
greater;  in  the  second,  our  means  of  research — the 
microscope  and  telescope,  the  spectroscope,  photography, 
and  many  other  ingenious  appliances — are  being  added 
to  and  rendered  more  effective  year  by  year ;  and,  above 
all,  the  circle  of  science  is  ever  widening,  so  that  the 
farther  we  advance  the  more  numerous  are  the  problems 
opening  out  before  us. 

No  doubt  there  are  other  Scientific  Series,  but  it  is 
not  believed  that  the  present  will  exactly  compete  with 
any  of  them.  The  International  Scientific  Series  and 
Nature  Series  are  no  doubt  useful  and  excellent,  and 
gome  of  the  volumes  contained  in  them  would  well 
carry  out  the  ideas  of  the  Publishers,  but,  as  a  rule,  they 
are  somewhat  more  technical  and  go  into  minuter  de- 
tails. 

The  names  of  the  Authors  are  a  sufficient  guarantee 
that  the  subjects  will  be  treated  in  an  interesting  and 
thoroughly  scientific  manner. 

HIGH  ELMS,  FARJTBOROUGH  : 
November,  1891. 


CONTENTS. 


CHAPTER  PAGE 

INTRODUCTION 1 

L— THE  ACORN  AND  ITS  GERMINATION— THE  SEEDLING  .    10 
II.— THE  SEEDLING  AND  YOUNG  PLANT    .        .        .        .24 
III.— THE  SEEDLING  AND  YOUNG  PLANT  (continued).    ITS 

SHOOT-SYSTEM — DISTRIBUTION  OF  THE  TISSUES        .    39 
IV.— THE    SEEDLING    AND    YOUNG    PLANT    (continued). 

STRUCTURE  OF  THE  VASCULAR  TISSUES,  ETC.         .    52 
V.— THE  SEEDLING  AND  YOUNG  PLANT  (continued).    THE 

BUDS  AND  LEAVES .72 

VI.— THE  TREE— ITS  ROOT-SYSTEM 89 

VII.— THE  TREE— ITS  SHOOT-SYSTEM 98 

VIII.— THE  TREE  (continued).     INFLORESCENCE  AND  FLOW- 
ERS— FRUIT  AND  SEED 121 

IX.— OAK   TIMBER— ITS   STRUCTURE  AND   TECHNOLOGICAL 

PECULIARITIES 136 

X.— THE  CULTIVATION  OF   THE  OAK,  AND  THE  DISEASES 

AND  INJURIES  TO  WHICH  IT  is  SUBJECT  .        .        .  147 

XL — RELATIONSHIPS   OF  THE  OAKS — THEIR  DISTRIBUTION 

IN  SPACE  AND  TIME  .  167 


THE    OAK. 


CHAPTER  I. 

INTRODUCTION. 

FAMOUS  in  poetry  and  prose  alike,  the  oak  must 
always  be  for  Englishmen  a  subject  of  interest,  around 
which  historical  associations  of  the  most  varied  character 
are  grouped ;  but  although  what  may  be  termed  the  sen- 
timental aspect  of  the  "  British  oak  "  is  not  likely  to  dis- 
appear even  in  these  days  of  iron-clads  and  veneering,  it 
must  be  allowed  that  the  popular  admiration  for  the 
sturdy  tree  is  to-day  a  very  different  feeling  from  the 
veneration  with  which  it  was  regarded  in  ancient  times ; 
and  that,  with  the  calmer  and  more  thoughtful  ways  of 
looking  at  this  and  other  objects  of  superstition,  a  cer- 
tain air  of  romance  seems  to  have  disappeared  which 
to  so  many  would  still  present  a  tempting  charm.  It  is 
not  to  these  latter  alone  that  our  few  existing  ancient 
oaks  are  so  attractive,  however,  and  a  slight  acquaint- 
ance with  the  oaken  roofs  and  carvings  of  some  of  our 
historical  edifices  affords  ample  proof  that  the  indefin- 
able charm  exercised  on  us  by  what  has  proved  so  last- 
ing, is  a  real  one  and  deep-seated  in  the  Saxon  nature. 


2  THE  OAK. 

In  fact,  everything  about  the  oak  is  suggestive  of 
durability  and  sturdy  hardiness,  and,  like  so  many 
objects  of  human  worship  in  the  earlier  days  of  man's 
emergence  from  a  savage  state,  the  oak  instinctively 
attracts  us.  The  attraction  is  no  doubt  complex,  tak- 
ing its  origin  in  the  value  of  its  acorns  and  timber 
to  our  early  forefathers,  not  unaffected  by  the  artistic 
beauty  of  the  foliage  and  habit  of  the  tree,  and  the 
forest  life  of  our  ancestors,  to  say  nothing  of  the  more 
modern  sentiment  aroused  when  ships  of  war  were  built 
almost  entirely  of  heart  of  oak;  for  the  Aryan  race 
seems  to  have  used  and  valued  both  the  fruit  and  the 
wood  from  very  early  times,  and  both  Celt  and  Saxon 
preserved  the  traditional  regard  for  them.  Memories  of 
our  Anglo-Saxon  ancestors  are  still  found  in  the  English 
and  German  names  for  the  tree  and  its  fruit,  as  seen  by 
comparing  the  Anglo-Saxon  dc  or  cec,  the  name  of  the 
oak,  with  the  English  word,  and  with  the  German  Eiclie 
on  the  one  hand,  and  with  acorn  (EicheT)  on  the  other. 
In  early  days,  moreover,  there  were  vast  oak  forests  in 
our  island  and  on  the  Continent,  and,  although  these 
have  been  almost  cleared  away  so  far  as  England  is  con- 
cerned, there  are  still  ancient  oaks  in  this  country,  some 
of  which  must  date  from  Saxon  times  or  thereabouts  '•> 
and  the  oak  is  still  one  of  the  commonest  trees  in 
France,  parts  of  Germany,  and  some  other  districts  in 
Europe. 

This  is  not  the  place  to  go  further  into  what  may  be 
called  the  folk-lore  of  the  oak — a  subject  which  would 


INTRODUCTION.  3 

supply  material  for  a  large  volume — but  it  may  be  re- 
marked that  giant  or  veteran  oaks  are  still  to  be  found 
(or  were  until  quite  recently)  in  Gloucestershire,  York- 
shire, and  on  Dartmoor  and  other  places,  and  a  very 
fair  idea  of  what  an  old  oak  forest  must  have  been  like 
may  be  gathered  from  a  visit  to  the  New  Forest  in 
Hampshire,  or  even  to  some  parts  of  Windsor  Forest. 

As  so  often  happens  in  the  study  of  science,  we  have 
in  the  oak  a  subject  for  investigation  which  presents 
features  of  intense  interest  at  every  turn ;  and  however 
much  the  new  mode  of  looking  at  the  tree  may  at  first 
sight  appear  to  be  opposed  to  the  older  one,  it  will  be 
found  that  the  story  of  the  oak  as  an  object  of  biological 
study  is  at  least  not  less  fascinating  than  its  folk-lore. 
With  this  idea  in  view,  I  propose  to  set  before  the 
reader  in  the  following  chapters  a  short  account  of  what 
is  most  worth  attention  in  the  anatomy  and  physiology 
of  the  oak,  as  a  forest  tree  which  has  been  so  thoroughly 
investigated  that  we  may  confidently  accept  it  as  a 
type. 

In  carrying  out  this  idea  there  are  several  possible 
modes  of  procedure,  but  perhaps  the  following  will  rec- 
ommend itself  as  that  best  adapted  to  the  requirements 
of  a  popular  book,  and  as  a  natural  way  of  tracing  the 
various  events  in  the  life-history  of  a  plant  so  complex 
as  is  the  tree. 

First,  the  acorn  will  be  described  as  an  object  with 
a  certain  structure  and  composition,  and  capable  of 
behaving  in  a  definite  manner  when  placed  in  the 


4  THE   OAK. 

ground,  and  under  certain  circumstances,  in  virtue  of 
its  physiological  properties  and  of  the  action  of  the  en- 
vironment upon  its  structure.  The  germinated  acorn 
gives  rise  to  the  seedling  or  young  oak,  and  \ve  shall 
proceed  to  regard  this,  again,  as  a  subject  for  botanical 
study.  It  consists  of  certain  definite  parts  or  organs, 
each  with  its  peculiar  structure,  tissues,  etc.,  and  each 
capable  of  behaving  in  a  given  manner  under  proper 
conditions.  The  study  of  the  seedling  leads  naturally 
to  that  of  the  sapling  and  the  tree,  and  the  at  first 
comparatively  simple  root-system,  stem,  and  leaves,  now 
become  complex  and  large,  and  each  demands  careful  at- 
tention in  order  that  we  may  trace  the  steps  by  which  the 
tree  is  evolved  from  the  plantlet.  A  section  will  there- 
fore be  devoted  to  the  root-system  of  the  tree,  its  disposi- 
tion, structure,  functions,  and  accessories ;  another  sec- 
tion will  be  occupied  in  describing  the  trunk,  branches, 
buds,  and  leaves,  and  their  co-relations  and  functions  ; 
the  inflorescence  and  flowers  will  demand  the  space  of 
another  chapter,  and  then  it  will  be  necessary  to  treat 
of  various  matters  of  importance  in  separate  chapters  as 
follows:  The  timber  must  be  considered  with  respect 
to  its  composition,  structure,  uses,  and  functions ;  then 
the  cortex  and  bark  have  to  be  described  and  their 
origin  and  development  explained.  These  subjects  nat- 
urally lead  to  that  of  the  growth  in  thickness  of  the 
tree — a  matter  of  some  complexity,  and  not  to  be  under- 
stood without  the  foregoing  knowledge  of  structure. 
Following  what  has  been  said  concerning  the  normal 


INTRODUCTION.  5 

structure  and  life-processes  of  the  tree,  we  may  turn  to 
the  investigation  of  its  cultivation  and  the  diseases 
which  attack  it,  concluding  with  a  necessarily  brief 
chapter  on  the  systematic  position  of  the  British  oak 
and  its  immediate  allies,  and  some  remarks  on  its  geo- 
graphical distribution  at  the  present  time. 

Of  course,  many  points  which  will  turn  up  in  the 
course  of  the  exposition  will  have  to  be  shortly  dealt 
with,  as  the  object  of  the  book  is  to  touch  things  with 
a  light  hand ;  but  it  is  hoped  that,  this  notwithstand- 
ing, the  reader  may  obtain  a  useful  glimpse  into  the 
domain  of  modern  botanical  science  and  the  problems 
with  which  forest  botany  is  concerned,  and  with  which 
every  properly  trained  forester  ought  to  be  thoroughly 
acquainted. 

The  oak,  as  is  well  known,  is  a  slow-growing,  di- 
cotyledonous tree  of  peculiar  spreading  habit,  and  very 
intolerant  of  shade  (Plate  I).  It  may  reach  a  great  age 
— certainly  a  thousand  years — and  still  remain  sound  and 
capable  of  putting  forth  leafy  shoots. 

The  root-system  consists  normally  of  a  deep  princi- 
pal or  tap  root  and  spreading  lateral  roots,  which  be- 
come very  thick  and  woody  and  retain  a  remarkably 
strong  hold  on  the  soil  when  the  latter  is  a  suitable 
deep,  tenacious  loam  with  rocks  in  it.  They  are  intol- 
erant of  anything  like  stagnant  water,  however,  and  will 
succeed  better  in  sandy  loam  and  more  open  soils  than 
in  richer  ones  improperly  drained. 

The  shoot-system  consists  of  the  stem  and  all  that  it 


6  THE   OAK. 

supports.  The  stem  or  trunk  is  usually  irregular  when 
young,  but  becomes  more  symmetrical  later,  and  after 
fifty  years  or  so  it  normally  consists  of  a  nearly  straight 
and  cylindrical  shaft  with  a  broad  base  and  spreading 
branches.  The  main  branches  come  out  at  a  wide 
angle,  and  spread  irregularly,  with  a  zigzag  course,  due 
to  the  short  annual  growths  of  the  terminal  shoots  and 
the  few  axillary  buds  behind,  and  also  to  the  fact  that 
many  of  the  axillary  lateral  buds  develop  more  slowly 
than  their  parent  shoot,  and  are  cut  off  in  the  autumn. 
Another  phenomenon  which  co-operates  in  producing 
the  very  irregular  spreading  habit  of  the  branches  is 
the  almost  total  suppression  of  some  of  the  closely- 
crowded  buds ;  these  may  remain  dormant  for  many 
years,  and  then,  under  changed  circumstances,  put 
forth  accessory  shoots.  Such  shoots  are  very  com- 
monly seen  on  the  stems  and  main  branches  of  large 
oaks  to  which  an  increased  accession  of  light  is  given 
by  the  thinning  out  of  surrounding  trees. 

The  short  ovoid  buds  develop  into  shoots  so  short 
that  they  are  commonly  referred  to  as  tufts  of  leaves, 
though  longer  summer  shoots  often  arise  later.  The 
latter  are  also  called  Lammas  shoots.  The  crown  of 
foliage  is  thus  very  dense,  and  the  bright  green  of  the 
leaves  in  early  summer  is  very  characteristic,  especially 
in  connection  with  the  horizontal,  zigzag  spreading  of 
the  shoots. 

While  still  young  the  tree  is  apt  to  keep  its  dead 
leaves  on  the  branches  through  the  winter,  or  at  least 


Plate  II. 


THE  OAK  IN  WIXTER. 


INTRODUCTION.  7 

until  a  severe  frost  followed  by  a  thaw  brings  them 
down.  The  buds,  leaves,  and  flowers  are  all  much  at- 
tacked by  gall-forming  insects,  many  different  kinds 
being  found  on  one  and  the  same  tree. 

It  is  not  until  the  oak  is  from  sixty  to  a  hundred 
years  old  that  good  seeds  are  obtained  from  it.  Oaks 
will  bear  acorns  earlier  than  this,  but  they  are  apt  to  be 
barren.  A  curious  fact  is  the  tendency  to  produce  large 
numbers  of  acorns  in  a  given  favorable  autumn,  and 
then  to  bear  none,  or  very  few,  for  three  or  four  years 
or  even  longer.  The  twisted,  "  gnarled  "  character  of 
old  oaks  is  well  known,  and  the  remarkably  crooked 
branches  are  very  conspicuous  in  advanced  age  and  in 
winter  (Plate  II).  The  bark  is  also  very  rugged  in  the 
case  of  ancient  trees,  the  natural  inequalities  due  to  fis- 
sures, etc.,  being  often  supplemented  by  the  formation 
of  "  burrs." 

A  not  inconsiderable  tendency  to  variation  is  shown 
by  the  oak,  and  foresters  distinguish  two  sub-species 
and  several  varieties  of  what  we  regard  (adopting  the 
opinion  of  English  systematic  botanists)  as  the  single 
species  Quercus  robur. 

Besides  forms  with  less  spreading  crowns,  the  spe- 
cies is  frequently  broken  up  into  two — Q.  pedunculata, 
with  the  female  flowers  in  rather  more  lax  spikes,  and 
the  acorns  on  short  stalks,  the  leaves  sessile  or  nearly  so, 
and  not  hairy  when  young;  and  Q.  sessiliflora,  with 
more  crowded  sessile  female  flowers,  and  leaves  on  short 
petioles  and  apt  to  be  hairy.  Other  minute  characters 


8  THE    OAK. 

have  also  been  described,  but  it  is  admitted  that  the 
forms  vary  much,  and  it  is  very  generally  conceded  that 
these  two  geographical  race-forms  may  be  united  with 
even  less  marked  varieties  into  the  one  species  Quercus 
robur. 

The  amount  of  timber  produced  by  a  sound  old  oak 
is  very  large,  although  the  annual  increment  is  so  re- 
markably small.  This  increment  goes  on  increasing 
slightly  during  the  first  hundred  years  or  so,  and  then 
falls  off;  but  considerable  modifications  in  both  the 
habit  of  the  tree  and  in  the  amount  of  timber  produced 
annually,  result  from  different  conditions.  Trees  grown 
in  closely-planted  preserves,  for  instance,  shoot  up  to 
great  heights,  and  develop  tall,  straight  trunks  with  few 
or  no  branches  ;  and  considerable  skill  in  the  forest- 
er's art  is  practiced  in  removing  the  proper  number 
of  trees  at  the  proper  time,  to  let  in  the  light  and  air 
necessary  to  cause  the  maximum  production  of  straight 
timber. 

Oaks  growing  in  the  open  air  are  much  shorter, 
more  branched  and  spreading,  and  form  the  peculiar 
dense,  twisted  timber  once  so  valuable  for  ship-building 
purposes.  Such  exposed  trees,  other  things  being  equal, 
develop  fruit  and  fertile  seeds  thirty  or  forty  years 
sooner  than  those  growing  in  closed  plantations. 

The  timber  itself  is  remarkable  for  combining  so 
many  valuable  properties.  It  is  not  that  oak  timber  is 
the  heaviest,  the  toughest,  the  most  beautiful,  etc.,  of 
known  woods,  but  it  is  because  it  combines  a  good  pro- 


INTRODUCTION.  9 

portion  of  weight,  toughness,  durability,  and  other  qual- 
ities that  it  is  so  valuable  for  so  many  purposes.  The 
richness  of  the  cortex  in  tannin  warranted  the  growing 
of  young  oaks  at  one  time  for  the  bark  alone,  and  the 
value  of  the  acorns  for  feeding  swine  has  been  immense 
in  some  districts. 


CHAPTER  II. 

THE    ACORN    AND    ITS    GERMINATION — THE    SEEDLING. 

WHEN  the  acorns  are  falling  in  showers  from  the 
oaks  in  October  and  November,  everybody  knows  that 
each  of  the  polished  leather-brown,  long,  egg-shaped 
bodies  tumbles  out  from  a  cup-like,  scaly  investment 
which  surrounded  its  lower  third  at  the  broader  end. 
Perhaps  everybody  would  not  be  certain  as  to  whether 
the  detached  acorn  is  a  seed  or  a  fruit,  so  I  anticipate 
the  difficulty  by  stating  at  the  outset  that  the  acorn  is 
the  fruit  of  the  oak,  and  contains  the  seed  within  its 
brown  shell ;  and  I  propose  to  commence  our  studies  by 
examining  an  acorn,  deferring  the  explanation  of  some 
minute  details  of  structure  until  we  come  to  trace  the 
origin  of  the  fruit  and  seed  in  the  flower. 

The  average  size  of  the  fruit  is  about  15  to  20  mm., 
or  nearly  three  quarters  of  an  inch,  long,  by  8  to  10 
mm.,  or  nearly  one  third  of  an  inch,  broad  at  the  middle 
of  its  length ;  the  end  inserted  in  the  cup  or  cupule  is 
broad  and  nearly  flat,  and  marked  by  a  large  circular 
scar  (Fig.  2,  s)  denoting  the  surface  of  attachment  to 
the  cupule.  This  scar  is  rough,  and  exhibits  a  number 
of  small  points  which  have  resulted  from  the  breaking 


THE   ACORN   AND   ITS   GERMINATION. 


11 


of  some  extremely  delicate  groups  of  minute  pipes, 
called  vascular  bundles,  which  placed  the  acorn  in  com- 
munication with  the  cup  and  tke  tree  previous  to  the 


FIG.  1. — Sprigs  of  oak,  showing  the  habit  and  the  arrangement  of  the 
acorns,  etc.,  in  September.    (After  Kotschy.) 


12  THE   OAK. 

ripening  of  the  former.  At  the  more  pointed  free  end 
of  the  acorn  is  a  queer  little  knob,  which  is  hard  and 
dry,  and  represents  the  mummified  remains  of  what  was 
the  stigma  of  the  flower,  and  which  lost  its  importance 
several  months  previously,  after  receiving  the  pollen. 

The  outer  hard  coat  of  the  acorn  is  a  tough,  leather- 
brown  polished  skin,  with  fine  longitudinal  lines  on  it, 
and  it  forms  the  outer  portion  of  the  true  covering  of 
the  fruit,  called  the  pericarp  (Fig.  2,  p).  On  removing 
it  we  find  a  thin,  papery  membrane  inside,  adhering 
partly  to  the  above  coat  and  partly  to  the  seed  inside. 
This  thin,  shriveled,  papery  membrane  is  the  inner  part 
of  the  pericarp,  and  the  details  of  structure  to  be  found 
in  these  layers  may  be  passed  over  for  the  present  with 
the  remark  that  they  are  no  longer  living  structures, 
but  exist  simply  as  protective  coverings  for  the  seed 
inside. 

The  centre  of  the  acorn  is  occupied  more  or  less 
entirely  by  a  hard  brown  body — the  seed — which  usual- 
ly rattles  about  loosely  on  shaking  the  ripe  fruit,  but 
which  was  previously  attached  definitely  at  the  broad 
end.  A  similar  series  of  changes  to  those  which  brought 
about  the  separation  of  the  acorn  from  the  cup — name- 
ly, the  shriveling  up  of  the  tiny  connecting  cords, 
etc. — also  caused  the  separation  of  the  seed  from  the 
pericarp,  and  we  may  regard  the  former  as  a  distinct 
body. 

Its  shape  is  nearly  the  same  as  that  of  the  acorn  in 
which  it  loosely  fits,  and  it  is  usually  closely  covered 


THE  ACORN  AND  ITS   GERMINATION. 


13 


with  a  thin,  brown,  wrinkled,  papery  membrane,  which 
is  its  own  coat — the  seed-coat,  or  testa  (Fig.  2,  t).  The 
extent  to  which  the  testa  remains  adherent  to  the  seed, 
or  to  the  inner  coat  of  the  pericarp,  and  both  together 
to  the  harder  outer  coat  of  the  pericarp,  need  not  be 

C. 
I 


FIG.  2.— Sections  of  acorns  in  three  planes  at  right  angles  to  one  an- 
other. A,  transverse ;  B,  longitudinal  in  the  plane  of  the  cotyledons, 
(1) ;  C,  longitudinal  across  the  plane  of  the  cotyledons  ;  c,  cotyledons ; 
t,  testa ;  p,  pericarp ;  s,  scar,  and  /•,  radicle  ;  pi,  plumule.  The  radicle, 
plumule,  and  cotyledons  together  constitute  the  embryo.  The  em- 
bryonic tissue  is  at  r  and  pi.  The  dots  in  A,  and  the  delicate  veins 
ill  E  and  C,  are  the  vascular  bundles. 

commented  upon  further  than  to  say  that  differences  in 
this  respect  are  found  according  to  the  completeness 
and  ripeness  of  the  acorn. 

Enveloped  in  its  testa  and  in  the  pericarp,  then,  we 
find  the  long  acorn-shaped  seed,  which  seems  at  first  to 
be  a  mere  horn-like  mass  without  parts.  This  is  not 
the  case,  however,  as  may  easily  be  observed  by  cutting 
the  mass  across,  or,  better  still,  by  first  soaking  it  in 
water  for  some  hours ;  it  will  then  be  found  that  the 


14-  THE   OAK. 

egg-shaped  body  consists  chiefly  of  two  longitudinal 
halves,  separated  by  a  median  plane  which  runs  through 
the  acorn  from  top  to  bottom.  These  two  halves,  lying 
face  to  face  so  closely  that  it  requires  the  above  manipu- 
lation to  enable  us  to  detect  the  plane  of  separation 
(Fig.  2,  Z),  are  not  completely  independent,  however;  at 
a  point  near  the  narrower  end  each  of  them  is  attached 
to  the  side  of  a  small  peg-shaped  body,  with  a  conical 
pointed  end  turned  towards  the  narrow  end  of  the 
acorn.  This  tiny  peg-shaped  structure  is  so  small  that 
it  may  be  overlooked  unless  some  little  care  is  exercised, 
but  if  the  hard  masses  are  completely  torn  apart  it  will 
be  carried  away  with  one  of  them. 

The  two  large  plano-convex  structures  are  called  the 
cotyledons,  or  seed-leaves  (Fig.  2,  c),  and  they,  together 
with  the  small  peg-shaped  body,  constitute  the  embryo 
of  the  oak.  The  peg-shaped  body  presents  two  ends 
which  project  slightly  between  the  two  cotyledons  be- 
yond the  points  of  attachment  to  them ;  the  larger  of 
these  ends  has  the  shape  of  a  conical  bullet,  and  is  di- 
rected so  that  its  tip  lies  in  the  point  of  the  narrower 
part  of  the  acorn ;  the  other,  and  much  smaller  end,  is 
turned  towards  the  broader  extremity  of  the  acorn.  The 
larger,  bullet-shaped  portion  is  termed  the  radicle  (Fig. 
2,  r),  and  will  become  the  primary  root  of  the  oak- 
plant  ;  the  smaller,  opposite  end  is  the  embryo  bud,  and 
is  termed  the  plumule  (Fig.  2,  pi],  and  it  is  destined  to 
develop  into  the  stem  and  leaves  of  the  oak.  If  the  ob- 
server takes  the  trouble  to  carefully  separate  the  two 


THE   ACORN   AND   ITS   GERMINATION.  15 

large  cotyledons,  without  tearing  them  away  from  the 
structures  just  described,  he  will  find  that  each  is  at- 
tached by  a  minute  stalk  to  a  sort  of  ridge  just  beneath 
the  tiny  plumule ;  this  ridge  is  sometimes  termed  the 
collar.  He  will  also  see  that  the  plumule  and  radicle 
fit  closely  into  a  cavity  formed  by  the  two  cotyledons, 
and  so  do  not  interfere  with  the  very  close  fitting  of 
their  two  flat  faces. 

Summing  up  these  essential  features  of  the  structure 
of  the  ripe  acorn  and  its  contents,  we  find  that  the  fruit 
contains  within  its  pericarp  (which  is  a  more  or  less 
complex  series  of  layers,  of  which  the  outermost  is  hard) 
the  seed ;  that  this  seed  comprises  a  membranous  testa 
inclosing  an  embryo  ;  and  that  the  embryo  is  composed 
of  two  huge  cotyledons,  a  minute  radicle,  and  a  still 
more  minute  plumule ;  and  that  the  tip  of  the  radicle 
is  turned  towards  the  pointed  end  of  the  acorn,  lying 
just  inside  the  membranes. 

Leaving  the  details  of  structure  of  the  membranes 
until  a  later  period,  when  we  trace  their  development 
from  the  flower,  I  must  devote  some  paragraphs  to  a 
description  of  the  minute  anatomy  and  the  contents  of 
the  embryo  as  found  in  the  ripe  acorn,  so  that  the 
process  of  germination  may  be  more  intelligible. 

Thin  sections  of  any  portion  of  the  embryo  placed 
under  the  microscope  show  that  it  consists  almost  en- 
tirely of  polygonal  chambers  or  cells,  with  very  thin 
membranous  walls,  and  densely  filled  with  certain  gran- 
ule-like contents.  These  polygonal  cells  have  not  their 


16  THE   OAK. 

own  independent  walls,  but  the  wall  which  divides  any 
two  of  them  belongs  as  much  to  one  as  to  the  other, 
and  only  here  and  there  do  we  find  a  minute  opening 
between  three  or  more  cells  at  the  corners,  and  pro- 
duced by  the  partial  splitting  of  the  thin  wall.  We 
may,  if  we  like,  regard  the  whole  embryo  as  a  single 
mass  of  material  cut  up  into  chambers  by  means  of  par- 
tition walls,  which  have  a  tendency  to  split  a  little  here 
and  there,  much  as  one  could  split  a  piece  of  pasteboard 
by  inserting  a  paper-knife  between  the  layers  composing 
it ;  what  we  must  not  do,  is  to  suppose  that  these  cells 
are  so  many  separate  chambers  which  have  been  brought 
into  juxtaposition.  In  other  words,  the  cell-wall  sepa- 
rating any  two  of  the  chambers  is  in  its  origin  a  whole, 
common  to  both  chambers,  and  the  plane  which  may  be 
supposed  to  divide  the  limits  of  each  is  imaginary  only. 

I  have  said  that  the  embryo  consists  almost  entirely 
of  this  mass  of  polygonal,  thin-walled  cells,  and  such  is 
called  fundamental  tissue;  but  here  and  there,  in  very 
much  smaller  proportion,  we  shall  find  other  structures. 
Surrounding  the  whole  of  the  embryo,  and  following 
every  dip  and  projection  of  its  contours,  will  be  found 
a  single  layer  of  cells  of  a  flattened,  tabular  shape,  and 
fitting  close  together  so  as  to  constitute  a  delicate  mem- 
brane or  skin  over  the  whole  embryo ;  this  outer  layer 
of  the  young  plant  is  called  the  epidermis. 

"Whenever  the  cotyledons,  or  the  radicle,  or  plumule 
are  cut  across  transversely  to  their  length,  there  are 
visible  certain  very  minute  specks,  which  are  the  cut 


THE   ACORN   AND   ITS   GERMINATION.  17 

surfaces  of  extremely  delicate  strands  or  cords  of  rela- 
tively very  long  and  very  narrow  cells,  the  minute 
structure  of  which  we  will  not  now  stay  to  investigate, 
but  simply  mention  that  these  extremely  fine  cords, 
running  in  the  main  longitudinally  through  the  em- 
bryo, are  termed  "  vascular  bundles "  (Fig.  2,  A).  It 
may  be  shown  that  there  is  one  set  of  them  running  up 
the  central  part  of  the  radicle,  starting  from  just  be- 
neath its  tip,  and  that  these  pass  into  the  two  coty- 
ledons, and  there  branch  and  run  in  long  strands  to- 
wards the  ends  of  the  latter. 

The  three  sets  of  structures  which  have  been  referred 
to  are  called  "  tissues,"  and  although  they  are  still  in  a 
very  young  and  undeveloped  condition,  we  may  say  that 
the  embryo  consists  essentially  of  a  large  amount  of 
thin- walled  cell-tissue  of  different  ages,  which  is  limit- 
ed by  an  epidermal  tissue  and  transversed  by  vascular 
tissue.  At  the  tips  of  the  radicle  and  plumule  the  cell- 
tissue  is  in  a  peculiar  and  young  condition,  and  is 
known  as  embryonic  tissue. 

As  regards  the  contents  and  functions  of  these 
tissues,  the  following  remarks  may  suffice  for  the  pres- 
ent. The  polygonal  cells  of  the  fundamental  tissue  of 
the  cotyledons  are  crowded  with  numerous  brilliant 
starch  grains,  of  an  oval  shape  and  pearly  luster,  and 
these  lie  imbedded  in  a  sort  of  matrix  consisting  chiefly 
of  proteids  and  tannin,  together  with  small  quantities 
of  fatty  substances. 

In  each  cell  there  is  a  small  quantity  of  protoplasm 


18  THE   OAK. 

and  a  nucleus,  but  this  latter  is  only  to  be  detected  with 
difficulty.  Certain  of  the  cells  contain  a  dark-brown 
pigment,  composed  of  substances  of  the  nature  of  tan- 
nin ;  and  small  quantities  of  a  peculiar  kind  of  sugar, 
called  quercite,  are  also  found  in  the  cells,  together  with 
a  bitter  substance. 

In  the  main,  the  above  are  stored  up  in  the  thin- 
walled  parenchyma  cells  as  reserve  materials,  intended 
to  supply  the  growing  embryo  or  seedling  with  nutri- 
tious food ;  the  starch  grains  are  just  so  many  packets 
of  a  food  substance  containing  carbon,  hydrogen,  and 
oxygen  in  certain  proportions  -,  the  proteids  are  similarly 
a  supply  of  nitrogenous  food,  and  minute  but  necessary 
quantities  of  certain  mineral  salts  are  mixed  with  these. 
The  vascular  bundles  are  practically  pipes  or  conduits 
which  will  convey  these  materials  from  the  cotyledons 
to  the  radicle  and  plumule  as  soon  as  germination 
begins,  and  I  shall,  say  no  more  of  them  here,  beyond 
noting  that  each  strand  consists  chiefly  of  a  few  very 
minute  vessels  and  sieve-tubes.  The  young  epidermis 
takes  no  part  either  in  storing  or  in  conducting  the 
food  substances  ;  it  is  simply  a  covering  tissue,  and  will 
go  on  extending  as  the  seedling  develops  a  larger  and 
larger  surface. 

We  are  now  in  a  position  to  inquire  into  what  takes 
place  when  the  acorn  is  put  into  the  soil  and  allowed  to 
germinate.  In  nature  it  usually  lies  buried  among  the 
decaying  leaves  on  the  ground  during  the  winter,  and  it 
may  even  remain  for  nearly  a  year  without  any  con- 


THE  ACORN   AND   ITS  GERMINATION.  19 

spicuous  change  ;  and  in  any  case  it  requires  a  period  of 
rest  before  the  presence  of  the  oxygen  of  the  air  and 
the  moisture  of  the  soil  are  effective  in  making  it  ger- 
minate— a  fact  which  suggests  that  some  profound  mo- 
lecular or  chemical  changes  have  to  be  completed  in  the 
living  substance  of  the  cells  before  further  activity  is 
possible.  We  have  other  reasons  for  believing  that  this 
is  so,  and  that,  until  certain  ferments  have  been  pre- 
pared in  the  cells,  their  protoplasm  is  unable  to  make 
use  of  the  food  materials,  and  consequently  unable  to 
initiate  the  changes  necessary  for  growth. 

Sooner  or  later,  however,  and  usually  as  the  temper- 
ature rises  in  spring,  the  embryo  in  the  acorn  absorbs 
water  and  oxygen,  and  swells,  and  the  little  radicle 
elongates  and  drives  its  tip  through  the  ruptured  in 
vestments  at  the  thin  end  of  the  acorn,  and  at  once 
turns  downward,  and  plunges  slowly  into  the  soil 
(Fig.  3).  This  peculiarity  of  turning  downward  is  so 
marked  that  it  manifests  itself  no  matter  in  what  posi- 
tion the  acorn  lies,  and  it  is  obviously  of  advantage  to 
the  plant  that  the  radicle  should  thus  emerge  first,  and 
turn  away  from  the  light,  and  grow  as  quickly  as  pos- 
sible towards  the  center  of  the  earth,  because  it  thus 
establishes  a  first  hold  on  the  soil,  in  readiness  to  absorb 
water  and  dissolve  mineral  substances  by  the  time  the 
leaves  open  and  require  them. 

The  two  cotyledons  remain  inclosed  in  the  coats  of 
the  acorn,  and  are  not  lifted  up  into  the  air ;  the  de- 
veloping root  obtains  its  food  materials  from  the  stores 


20 


THE  OAK. 


in  the  cells  of  the  cotyledons,  as  do  all  the  parts  of  the 
young  seedling  at  this  period.     In  fact,  these  stores  in 


Fio.  8. — I.  Longitudinal  section  through  the  posterior  half  of  the  em- 
bryo, in  a  plane  at  right  angles  to  the  plane  of  separation  between  the 
cotyledons  (slightly  magnified).  II.  Germinating  embryo,  with  one 
cotyledon  removed.  III.  Acorn  in  an  advanced  stage  of  germination, 
a,  the  scar ;  #,  pericarp ;  «A,  testa ;  5,  plumule ;  st,  petioles  of  coty- 
ledons, from  between  which  the  plumule,  J,  emerges ;  he,  hypocotyl ; 
c,  cotyledons ;  /,  vascular  bundles ;  w,  radicle  (primary  root) ;  w',  sec- 
ondary roots.  Root-hairs  are  seen  covering  the  latter  and  the  anterior 
part  of  the  primary  root  in  III.  (After  Sachs.) 


THE   ACORN   AND   ITS   GERMINATION.  21 

the  cotyledons  contribute  to  the  support  of  the  baby 
plant  for  many  months,  and  even  two  years  may  elapse 
before  they  are  entirely  exhausted. 

When  the  elongated  radicle,  or  primary  root,  has 
attained  a  length  of  two  or  three  inches  in  the  soil,  and 
its  tip  is  steadily  plunging  with  a  very  slight  rocking 
movement  deeper  and  deeper  into  the  earth,  the  little 
plumule  emerges  from  between  the  very  short  stalks  of 
the  cotyledons  (Fig.  3,  st),  which  elongate  and  separate 
to  allow  of  its  exit,  and  grows  erect  into  the  light  and 
air  above  ground.  It  will  be  understood  that  this  plu- 
mule also  is  living  at  the  expense  of  the  food  stores  in 
the  cotyledons,  the  dissolved  substances  passing  up  into 
it  through  the  tiny  vascular  bundles  and  cells,  as  they 
have  all  along  been  passing  down  to  the  growing  root 
through  the  similar  channels  in  its  tissues. 

The  plumule — or,  as  we  must  now  call  it,  primary 
shoot — differs  from  the  root  not  only  in  its  more  tardy 
growth  at  first,  but  also  in  its  habit  of  growing  away 
from  the  center  of  gravitation  of  the  earth  and  into  the 
light  and  air ;  and  here,  again,  we  have  obviously  adap- 
tations which  are  of  advantage  to  the  plant,  which 
would  soon  be  top-heavy,  moreover,  if  the  shoot  were 
far  developed  before  the  root  had  established  a  hold- 
fast in  the  soil. 

The  little  oak  shoot  is  for  some  time  apparently 
devoid  of  leaves  (Fig.  4),  but  a  careful  examination 
shows  that  as  it  elongates  it  bears  a  few  small  scattered 
scales,  like  tiny  membranes,  each  of  which  has  a  very 


22 


THE   OAK. 


minute  bud  in  its  axil.  When  the  primary  shoot  has 
attained  a  length  of  about  three  inches  there  are  usually 
two  of  these  small  scale-leaves  placed  nearly  opposite 
one  another  close  to  the  tip,  and  a  little  longer  and  nar- 
rower than  those  lower  down  on 
the  shoot  ;  from  between  these 
two  linear  structures  the  first 
true  green  foliage  leaf  of  the 
oak  arises,  its  short  stalk  being 
flanked  by  them.  This  first  leaf 
is  small,  but  the  tip  of  the  shoot 
goes  on  elongating  and  throwing 
out  others  and  larger  ones,  until 
by  the  end  of  the  summer  there 
are  about  four  to  six  leaves 
formed,  each  with  its  minute 
stalk  flanked  by  a  pair  of  tiny 
linear  scales  ("stipules,"  as  they 
are  called)  like  those  referred  to 
above. 

Each  of  the  green  leaves  arises 

FIG.  4. — Germinating  acorn, 

showing  the  manner  of  from  a  point  on  the  young  stem 
emergence  of  the  pri-  whjch  ig  a  Httle  hj  h  and  more 
mary  shoot,  and  the  first  ° 

scales  (stipules)  on  the  to  one  side,  than  that  from  which 
latter.  (After  Kossmass-  the  lowermost  one  springs ;  hence 
a  line  joining  the  points  of  inser- 
tion of  the  successive  leaves  describes  an  open  spiral 
round  the  shoot  axis — i.  e.,  the  stem — and  this  of  such 
a  kind  that  when  the  spiral  comes  to  the  sixth  leaf  up- 


THE  ACORN  AND  I/S   GERMINATION.  23 

ward  it  is  vertically  above  the  first  or  oldest  leaf  from 
which  we  started,  and  has  passed  twice  round  the  stem. 

At  the  end  of  this  first  year,  which  we  may  term 
the  period  of  germination,  the  young  oak-plant  or  seed- 
ling has  a  primary  root  some  twelve  to  eighteen  inches 
long,  and  with  numerous  shorter,  spreading  side  root- 
lets, and  a  shoot  from  six  to  eight  inches  high,  bearing 
five  or  six  leaves  as  described,  and  terminating  in  a 
small  ovoid  bud  (Figs.  3  and  4).  The  whole  shoot  is 
clothed  with  numerous  very  fine  soft  hairs,  and  there 
are  also  numerous  fine  root-hairs  on  the  roots,  and 
clinging  to  the  particles  of  soil.  The  tip  of  each  root  is 
protected  by  a  thin  colorless  cap — the  root-cap — the  de- 
scription of  which  we  defer  for  the  present. 

About  May,  in  the  second  year,  each  of  the  young 
roots  is  elongating  in  the  soil  and  putting  forth  new 
root-hairs  and  rootlets,  while  the  older  roots  are  thicken- 
ing and  becoming  harder  and  covered  with  cork ;  and 
each  of  the  buds  in  the  axils  of  the  last  year's  leaves 
begins  to  shoot  out  into  a  branch,  bearing  new  leaves  in 
its  turn,  while  the  bud  at  the  end  of  the  shoot  elongates 
and  lengthens  the  primary  stem,  the  older  parts  of 
which  are  also  becoming  thicker  and  clothed  with  cork. 
And  so  the  seedling  develops  into  an  oak-plant,  each 
year  becoming  larger  and  more  complex,  until  it  reaches 
the  stage  of  the  sapling,  and  eventually  becomes  a 
tree. 


CHAPTER  III. 

THE   SEEDLING   AND   YOUXG    PLANT. 

BEFORE  proceeding  to  describe  the  further  growth 
and  development  of  the  seedling,  it  will  be  well  to  ex- 
amine its  structure  in  this  comparatively  simple  stage, 
in  order  to  obtain  points  of  view  for  our  studies  at  a 
later  period.  For  many  reasons  it  is  advantageous  to 
begin  with  the  root-system.  If  we  cut  a  neat  section 
accurately  transverse  to  the  long  axis  of  the  root,  and  a 
few  millimetres  behind  its  tip,  the  following  parts  may 
be  discerned  with  the  aid  of  a  good  lens,  or  a  micro- 
scope, on  the  flat  face  of  the  almost  colorless  section.  A 
circular  area  of  grayish  cells  occupies  the  centre — this 
is  called  the  axis  cylinder  of  the  young  root  (Fig.  5,  A, 
a).  Surrounding  this  is  a  wide  margin  of  larger  cells, 
forming  a  sort  of  sheathing  cylinder  to  this  axial  one, 
and  termed  the  root-cortex.  The  superficial  layer  of 
cells  of  this  root-cortex  has  been  distinguished  as  a 
special  tissue,  like  an  epidermis,  and  as  it  is  the  layer 
which  alone  produces  the  root-hairs,  we  may  convenient- 
ly regard  it  as  worthy  of  distinction  as  the  piliferous 
layer  (Fig.  5,  e). 

Similar  thin  sections  a  little  nearer  the  tip  of  the 


THE  SEEDLING  AND  YOUNG  PLANT. 


25 


root  would  show  a  more  or  less  loose  sheath  of  cells  in 
addition  to  and  outside  this  piliferous  layer.  This  is 
the  root-cap,  which  is  a  thimble-shaped  sheath  of  looser 
cells  covering  the  tip  of  the  root  as  a  thimble  covers  the 


FIG.  5. — A.  Transverse  section  of  young  root  under  a  lens,  showing  the 
axis  cylinder,  a ;  epidermis  or  piliferous  layer,  e ;  and  the  cortex  be- 
tween. B.  The  same,  more  highly  magnified  :  c,  cortex ;  p,  phloem  ; 
a;,  xylem ;  C.  A  portion  still  more  highly  magnified :  pTi,  phloem ; 
j?,  pith ;  per,  pericycle ;  sA,  sheath  (endodermis) ;  other  letters  as 
before. 

nd  of  the  finger,  only  we  must  imagine  the  extreme  tipe 
of  the  finger  organically  connected  with  the  inside  of 
the  cap  to  make  the  analogy  suitable  (see  Fig.  6).  The 


26  THE   OAK. 

rest  of  the  section  would  be  much  as  before,  excepting 
that  the  distinction  between  the  axial  cylinder  and  the 
root-cortex  would  be  less  marked. 

Now  contrast  a  section  cut  a  couple  of  inches  or  so 
away  from  the  tip,  in  the  region  where  the  root-hairs 
are  well  developed.  Here  we  find  the  axial  cylinder 
much  more  strongly  marked  than  before,  and  the  pilif- 
erous  layer  is  very  clearly  distinguished  by  the  fact  that 
it  gives  off  the  root-hairs,  each  hair  arising  from  one  of 
its  cells. 

A  little  investigation  shows  that  the  axial  cylinder 
is  thus  strongly  marked  because  certain  dark-looking 
structures  have  now  been  formed  just  inside  its  boundary 
— i.  .e,  just  inside  the  line  which  delimits  it  from  the 
root-cortex.  These  dark  structures  are  the  sections  of 
several  fine  cords  or  bundles,  called  vascular  bundles, 
which  can  here  be  traced  up  and  down  in  the  root.  As 
the  section  shows,  these  bundles  are  arranged  at  approxi- 
mately equal  distances  in  a  cylinder;  they  form  the 
vascular  system  of  the  root,  and  they  always  run  along 
the  region  just  inside  the  outer  boundary  of  the  axial 
cylinder  (Fig.  5,  B,  p  and  x). 

If  we  compare  our  successive  transverse  sections,  and 
cut  others  at  various  levels  along  the  young  root,  it  will 
be  clear  that,  as  we  pass  from  the  tip  of  the  root  to 
parts  farther  behind,  certain  changes  must  be  going  on, 
which  result  first  in  the  definite  marking  out  of  the  axial 
cylinder,  and  then  in  the  development  of  these  vascular 
bundles  and  of  other  parts  we  will  not  describe  in  detail. 


THE  SEEDLING  AND  YOUNG  PLANT. 


27 


If,  in  addition  to  these  successive  transverse  sections, 
we  examine  a  carefully  prepared  longitudinal  section,  cut 
so  as  to  pass  accurately  through 
the  median  plane  of  the  root,  the 
comparison  not  only  establishes 
the  above  conclusion,  but  it  en- 
ables us  to  be  certain  of  yet  other 
facts  (Fig.-  6).  Such  a  section 
shows  the  root-cap  covering  the 
tip  as  a  thimble  the  end  of  the 
finger,  and  the  rim  of  this  root- 
cap  is  evidently  fraying  away  be- 
hind ;  the  cells  of  which  it  is 
composed  die  and  slough  off  as 
the  root  pushes  its  way  between 
the  abrading  particles  of  soil. 
Obviously  this  loss  of  worn-out 
tissue  must  be  made  good  in 
some  way,  and  closer  examination 

shows  how  this  occurs.     The  ex- 

\i*.c. 
treme  tip  of  the  root  proper  fits  ,-, 

FIG.  6.— Diagrammatic  sec- 

closely  into  the  cap,  and  evident-       tion  through  the  end  of 
ly  adds  cells  to  the  inside  of  the 
latter,  and  thus  replaces  the  old 
ones  which  are  worn  away.     At 
this  true  tip  of  the  root,  more- 
over, we  make  another  discovery, 
namely,   that  all   the   cells  are    there  alike  in  shape, 
size,  and  other  peculiarities ;  and  if  we  could  take  a 


the  root  of  the  oak.    c, 

root-cortex ;  e,  piliferous 
layer ;  re,  root-cap ;  ra, 
the  true  embryonic  tis- 
sue (so-called  "  growinsf- 
point ") ;  ph,  phloem ;  x, 
xylem. 


28  THE   OAK. 

transverse  section  exactly  at  this  place  we  should  see 
no  differentiation  into  axial  cylinder  and  root-cortex, 
etc.  ;  the  small  circular  mass  would  consist  of  cells 
all  alike,  and  with  very  thin  walls  and  full  of  dense 
protoplasm.  This  undifferentiated  formative  tissue  is 
called  the  embryonic  tissue  of  the  root  (Fig.  6,  m). 
A  little  behind  this  we  see  the  axis-cylinder  and  root- 
cortex  already  formed ;  still  farther  away  we  see  the 
vascular  bundles  appearing,  first  as  very  thin  cords,  and 
then  getting  stronger  and  stronger  as  we  recede  from 
the  tip  (Fig.  6,  ph  and  x) ;  and  similarly  we  trace  the 
gradual  development  of  the  other  parts  in  acropetal 
succession— i.  e.,  the  nearer  we  go  to  the  apex  the 
younger  the  parts  are. 

Now,  there  is  a  conclusion  of  some  importance  to  be 
drawn  from  the  putting  together  of  these  facts — namely, 
that  all  the  structures  found  between  the  embryonic 
tissue  at  the  tip  of  the  root  and  the  place  where  the  root 
joins  the  stem  have  been  gradually  formed  from  the 
embryonic  tissue  in  acropetal  succession.  We  may 
picture  this  by  marking  a  given  level  on  the  root, 
some  distance  away  from  the  tip,  where  the  axis-cyl- 
inder is  sharply  marked  and  has  well-developed  vascular 
bundles,  the  root-cortex  is  distinct,  and  the  piliferous 
layer  bears  root-hairs,  and  remembering  that  so  many 
days  or  weeks  ago  this  very  spot  was  in  the  then  grow- 
ing-point, and  consisted  of  embryonic  tissue  with  the 
cells  all  alike.  Or  we  may  put  it  in  a  different  way 
thus :  the  present  growing-point  consists  of  embryonic 


THE  SEEDLING  AND  YOUNG  PLANT.       29 

cells  all  alike ;  in  a  few  days  some  of  these  cells  will 
have  changed  into  constituents  of  the  axis-cylinder  and 
cortex,  and  subsequently  some  of  them  will  give  rise  to 
vascular  bundles,  etc.  Not  all,  however ;  and  it  is  neces- 
sary to  understand  that  as  the  embryonic  tissue  moves 
onward  and  leaves  the  structures  referred  to  in  its  wake, 
it  does  so  by  producing  new  embryonic  cells  in  front — 
i.  e.,  between  the  present  ones  and  the  root-cap. 

We  must  now  look  a  little  more  closely  into  the 
structure  of  the  axial  cylinder,  at  a  level  a  little  behind 
the  region  where  the  root-hairs  are  produced  on  the 
piliferous  layer. 

A  thin  transverse  section  in  this  region  shows  that 
the  root-hairs  have  all  died  away,  and  the  walls  of  the 
cells  of  the  piliferous  layer  are  becoming  discolored, 
being,  in  fact,  converted  into  a  brown,  cork -like  sub- 
stance impervious  to  moisture,  or  nearly  so ;  conse- 
quently the  piliferous  layer  is  no  longer  absorptive,  and 
it  will  soon  be  thrown  off,  as  we  shall  see. 

The  cortex  offers  little  to  notice,  except  that  its 
cells  are  being  passively  stretched  or  compressed  by  the 
growth  and  processes  going  on  in  the  axial  cylinder  ;  and 
it  is  this  cylinder  that  attracts  our  special  attention,  and 
several  points  not  noticed  before  must  now  be  examined 
in  some  detail. 

In  the  first  place,  the  cylinder  is  demarkated  off 
from  the  cortex  by  a  single  layer  of  cells  shaped  like 
bricks,  and  with  a  sort  of  black  dot  on  the  radial  walls  ; 
this  is  called  the  endodermis,  and  may  be  regarded  as  a 


30  THE   OAK. 

slieath  limiting  what  belongs  to  the  axis-cylinder  (Fig. 
5,  c,  sit).  Inside  this  endodermis  are  about  two  rows 
of  thin- walled  cells  full  of  protoplasm,  and  forming  a 
continuous  layer  beneath  the  endodermis.  This  layer  is 
termed  the  pericyde  (Fig.  5,  c,  per),  and  it  is  a  very 
important  structure,  because  its  cells  give  rise,  by  re- 
peated divisions,  to  the  lateral  rootlets,  which  then 
grow  out  and  burst  their  way  through  the  endodermis, 
cortex,  and  piliferous  layer,  and  so  reach  the  soil.  It  is, 
of  course,  necessary  to  bear  in  mind  that  the  endoder- 
mis and  pericycle  are  concentric  cylinders  superposed 
on  the  axis  of  the  root,  as  it  were,  and  only  appear  as 
rings  on  the  transverse  section. 

Inside  the  pericycle  are  arranged  the  vascular  bun- 
dles, and  we  shall  have  to  devote  a  few  words  of  ex- 
planation to  these  remarkable  and  somewhat  complex 
structures. 

The  section  shows  that  there  are  about  ten  alternat- 
ing groups  of  tissue  constituting  these  bundles,  and 
again  the  reader  must  bear  in  mind  that  each  group  is 
the  transverse  section  of  a  long  cord  running  up  and 
down  the  root.  Of  these  groups  five  are  much  more 
conspicuous  than  the  other  five,  because  they  consist 
chiefly  of  more  or  less  polygonal  openings  with  firm, 
dark  contours.  These  are  the  xylem  vessels  of  the  vas- 
cular bundles  (Fig.  5,  c,  a;),  and  we  must  note  the  fol- 
lowing facts  about  them  :  In  the  first  place,  they  are 
smaller  nearer  the  pericycle  than  they  are  nearer  the 
center  of  the  axial  cylinder,  and  the  comparison  of 


THE  SEEDLING  AND  YOUNG  PLANT.       31 

numerous  transverse  sections  at  different  levels  of  the 
root  would  prove  that  the  smallest  vessels  are  the  first 
to  develop ;  whence  we  learn  two  facts — namely,  that 
the  xylem  vessels  of  the  young  root  are  developed  in 
centripetal  order,  and  that  the  later  ones  have  a  larger 
caliber  than  those  formed  earlier. 

If  longitudinal  sections  are  compared  with  these 
transverse  ones — and  I  may  here  observe  that  it  is  only 
by  means  of  numerous  such  comparisons  that  these 
matters  have  been  gradually  discovered— it  is  found 
that  each  vessel  is  a  long  tube,  usually  containing  air 
and  water  when  complete,  the  lateral  walls  of  which  are 
curiously  and  beautifully  marked  with  characteristic 
thick  and  thin  ornamentation.  It  must  suffice  here  to 
say  that  the  small,  outer,  first-formed  vessels  are  marked 
with  a  spiral  thickening,  reminding  one  of  caoutchouc 
gas-tubing  kept  open  by  means  of  a  spiral  wire  inside  ; 
while  the  larger  ones,  developed  later,  usually  have 
numerous  small  pits  on  their  walls,  reminding  one  of 
mouths,  and  the  structure  of  which  is  very  curious. 
Consequently  these  groups  of  xylem  vessels  are  said  to 
consist  of  spiral  and  pitted  vessels,  and  their  chief  func- 
tion is  to  convey  water  up  the  root  to  the  stem  (cf.  Fig. 
16).  Packed  in  between  these  vessels  are  certain  cells 
known  as  the  wood-cells. 

Keturning  to  the  transverse  section,  we  saw  that 
between  each  xylem  group  described  above  there  is  a 
group  of  structures  differing  from  the  latter  in  their  less 
distinct  outlines ;  these  alternate  groups  are  known  as 


32  THE  OAK. 

phloem,  and  we  may  shortly  examine  the  elements  of 
which  they  are  composed,  as  before,  by  comparing  sec- 
tions of  various  kinds. 

Here,  again,  we  find  the  chief  structures  in  the 
phloem  are  also  vessels — i.  e.,  long,  tubular  organs— but 
very  different  in  detail  from  the  vessels  of  the  xylem. 

In  the  first  place,  their  walls  are  thin  and  soft,  and 
composed  of  the  unaltered  cellulose  which  is  so  charac- 
teristic of  young  cells  (instead  of  being  hard,  like  the 
lignified  walls  of  the  xylem  vessels) ;  then,  again,  they 
contain  protoplasm  and  other  organized  cell  contents, 
instead  of  merely  air  and  water.  Finally,  they  are  not 
so  completely  tubular  as  the  typical  xylem  vessels  are, 
because  the  transverse  septa  of  the  constituent  cells  are 
not  absorbed,  but  are  merely  pierced  by  fine  strands  of 
protoplasm,  and  therefore  look  like  sieves  when  viewed 
from  above — whence  the  name  "sieve-tubes."  In  the 
phloem  also  we  find  cells — phloem-cells — packed  in  be- 
tween the  sieve-tubes. 

If  we  shortly  summarize  the  above  we  find  that  the 
root  consists  of  an  axis-cylinder  surrounded  by  a  cortex 
and  the  piliferous  layer.  At  the  tip  the  whole  is  cov- 
ered by  the  root-cap,  which  is  organically  connected 
with  the  embryonic  tissue  which  forms  all  these  struct- 
ures. The  axis-cylinder  is  somewhat  complex ;  it  is 
sheathed  by  the  endodermis  and  the  pericyle,  the  lat- 
ter of  which  gives  origin  to  the  new  rootlets.  Inside 
the  pericycle  are  the  vascular  bundles  running  up  and 
down  as  separate,  alternate  cords  of  xylem  and  phloem  ; 


THE  SEEDLING  AND  YOUNG  PLANT. 


33 


FIG.  7. — Portion  of  young  growing  ends  of  more  advanced  root,  with  nu- 
merous rootlets.  Some  of  the  latter  are  much  branched  into  tuft-like 
collections,  m ;  these  form  the  so-called  Mycorhiza.  Natural  size. 


34  TEE   OAK. 

the  xylem  consists  of  vessels  and  cells,  the  former  de- 
veloped centripetally,  while  the  phloem  consists  of 
sieve-tubes  and  cells.  Any  cell-tissue  which  may  lie 
in  the  center  of  the  axial  cylinder,  and  surrounded  by 
the  vascular  bundles,  corresponds,  in  popular  language, 
to  pith ;  any  that  runs  between  the  bundles  corresponds 
to  medullary  rays. 

We  now  turn  to  the  root  as  a  whole,  and  examine  its 
behavior  in  the  soil  as  the  young  seedling  develops  fur- 
ther, and  in  the  light  of  the  above  anatomical  facts. 

Although  the  root-system  of  the  young  plant  is  reg- 
ularly constituted  of  a  series  of  lateral  rootlets  spring- 
ing from  the  primary  root,  the  orderly  arrangement  is 
soon  disturbed  when  the  tertiary  and  other  rootlets 
begin  to  develop  from  the  secondary  rootlets ;  more- 
over, as  the  age  of  the  tree  increases,  the  tendency  to 
irregularity  is  increased  owing  to  the  production  of 
rootlets  of  the  higher  orders  at  different  places,  thus 
interfering  with  the  acropetal  succession  of  the  younger 
rootlets. 

At  first  the  root-system  is  especially  engaged  in  bor- 
ing into  the  soil,  and,  provided  the  latter  is  sufficiently 
deep  and  otherwise  suitable,  the  tap-root  will  go  down 
a  foot  or  more  in  the  first  year.  As  the  roots  thick- 
en they  exhibit  considerable  plasticity,  as  is  especially 
evinced  on  rocky  ground,  where  the  older  roots  may 
often  be  found  in  cracks  in  the  rocks,  so  compressed  that 
they  form  mere  flattened  sheets  many  times  broader 
than  they  are  thick  (Fig.  8). 


THE  SEEDLING  AND  YOUNG  PLANT.       35 

It  has  already  been  men- 
tioned that  the  tip  of  the 
young  primary  root  circum- 
nutates,  and  Darwin  also 
found  that  the  tip  of  the 
radicle  is  extremely  sen- 
sitive to  the  irritation  of 
small  bodies  in  contact  with 
it.  It  is  also  positively  geo- 
tropic,  directing  itself  ver- 
tically downward  if  the  par- 
tially grown  radicle  is  laid 
horizontally  ;  and  it  may  be 
assumed  from  the  behavior 
of  other  plants  of  the  same 
kind  that  the  tip  of  the 
radicle  is  negatively  helio- 
tropic — i.  e.,  it  turns  away 
from  the  source  of  light. 
Whether  it  is  also  sensitive 
to  differences  in  the  degree 
of  moisture  on  different 
sides  (hydrotropic),  or  to 
differences  of  temperature 

FIG.  8.— Portion  of  an  older  root  of 

(  thermotropic  )»       IS        not        an  oak)  which  had  penetrated 

known,   but    it    may  be    in-         while  young  between  two  pieces 

of  hard  rock,  and  had  to  adapt 

f  erred    that    such    is    the       its  form  accordingly  as  it  thick- 
case  ;     nor     do    we    know       ene<L   <After  D6bner-} 
whether  it  is  affected  by  electric  currents  in  the  earth. 


36  THE   OAK. 

The  root  of  the  oak,  speaking  generally,  is  a  typical 
root  in  the  following  respects :  It  consists,  as  we  have 
seen,  of  a  primary  or  tap  root  which  develops  secondary 
or  lateral  roots  in  acropetal  succession,  and  these  in 
their  turn  produce  rootlets  of  a  higher  order.  These 
secondary,  tertiary,  etc.,  rootlets  arise  endogenously, 
taking  origin  from  the  pericycle  at  the  periphery  of  the 
strand  of  vascular  bundles  which  traverse  the  central 
axis,  and  then  bursting  through  the  cortex  to  the  ex- 
terior. The  primary  root,  as  well  as  the  rootlets  of  all 
orders,  are  provided  with  a  root-cap  at  the  tips,  and 
they  all  agree  in  being  devoid  of  chlorophyll  or  stomata. 
From  the  outer  layer  of  cells — the  piliferous  layer,  cor- 
responding to  an  epidermis — root-hairs  are  developed  at 
some  little  distance  behind  the  root-cap,  and  these  su- 
perficial cellular  outgrowths  also  rise  in  acropetal  suc- 
cession, the  older  ones  behind  dying  off  as  the  younger 
ones  arise  farther  forward.  If  we  bear  in  mind  all 
that  has  been  shortly  stated  above,  it  will  be  very  easy 
to  figure  the  behavior  of  the  root-system  as  it  pene- 
trates the  ground,  and  the  following  short  description 
of  the  biology  of  the  root  may  render  the  matter  clear. 
When  the  radicle  commences  to  bore  down  into  the  soil 
it  puts  forth  a  large  number  of  root-hairs  from  the 
parts  a  few  millimetres  behind  the  tip,  and  these  attach 
•themselves  to  the  particles  of  soil  and  supply  points  of 
resistance;  the  tip  of  the  radicle  is  protected  by  the 
slippery  root-cap,  and  it  must  be  borne  in  mind  that 
the  embryonic  tissue  of  the  growing-point  consists  of 


THE  SEEDLING  AND  YOUNG  PLANT.       37 

thin-walled  cells  full  of  relatively  stiff  protoplasm  with 
very  little  water.  Hence  the  growing-point  is  a  firm 
body.  The  most  active  growth  of  the  root  takes  place 
at  a  region  several  millimetres  behind  the  root-cap,  be- 
tween it  and  the  fixed  point  above  referred  to ;  hence 
the  apex  of  the  root  is  really  driven  into  the  ground 
between  the  particles  of  rock,  etc.,  of  which  the  latter 
is  composed.  This  driving  in  is  aided  by  the  negative 
heliotropism,  the  positive  geotropism,  the  circumnuta- 
tion,  and  other  irritabilities  of  the  apical  portions  of 
the  root,  and  it  bores  its  way  several  centimetres  down- 
ward. As  it  lengthens — by  the  addition  of  cells  pro- 
duced by  the  division  of  those  of  the  embryonic  tissue, 
and  by  their  successive  elongation — the  older  parts  be- 
hind go  on  producing  root-hairs,  and  thus  a  vertical 
cylinder  of  soil  around  the  primary  root  is  gradually 
laid  under  contribution  for  water  containing  dissolved 
salts,  etc.  In  those  parts  of  the  root  which  are  behind 
the  growing  region  no  further  elongation  occurs ;  hence 
the  tips  of  the  lateral  rootlets  (which  have  been  devel- 
oping in  the  pericycle  at  the  circumference  of  the  axial 
cylinder  of  vascular  bundles)  can  now  safely  break 
through  the  cortex  and  extend  themselves  in  the  same 
manner  from  the  parent  root  as  a  fixed  base,  without 
danger  of  being  broken  off  by  the  elongation  of  the 
growing  parts.  Each  of  these  secondary  rootlets  grows 
out  at  an  obtuse  angle  from  the  primary  root,  and  not 
vertically  downward,  and  as  it  does  so  a  similar  wave 
of  root-hairs  is  developed  along  it ;  thus  a  series  of 

4 


38  THE   OAK. 

nearly  horizontal  radiating  cylinders  of  soil  are  placed 
under  contribution  as  before.  Then  the  secondary  root- 
lets emit  tertiary  rootlets  in  all  directions — these  and 
the  rootlets  of  a  higher  order  growing  without  any  par- 
ticular reference  to  the  direction  of  gravitation,  light, 
etc. — and  so  place  successive  cylinders  of  soil  in  all  di- 
rections under  contribution  as  before.  By  this  time, 
however,  the  symmetry  of  the  root-system  is  being  dis- 
turbed because  some  of  the  rootlets  meet  with  stones  or 
other  obstacles,  others  get  dried  up  or  frozen,  or  gnawed 
off  or  otherwise  injured,  and  the  varying  directions  in 
which  new  growths  start  and  in  which  the  resistances 
are  least,  influence  the  very  various  shapes  of  the  tan- 
gled mass  of  roots  now  permeating  the  soil  in  all  direc- 
tion's. 

These  roots  supply  the  ever-increasing  needs  for 
water  of  the  shoot-system,  the  leaf -surface  of  which  is 
becoming  larger  and  larger,  and  as  the  greater  volume 
of  water  from  the  gathering  rootlets  has  all  to  enter  the 
stem  via  the  upper  part  of  the  main  root,  we  are  not 
surprised  to  find  that  the  latter  thickens,  as  does  the 
stem ;  and  so  with  all  the  older  roots — they  no  longer 
act  as  absorbing  roots,  but  become  merely  larger  and 
larger  channels  for  water,  and  girder-like  supporting 
organs. 


CHAPTER  IV. 

THE    SEEDLIXG    AXD   YOUNG    PLANT    (continued}. 

ITS  SHOOT-SYSTEM — DISTRIBUTION  OF  THE  TISSUES. 

I  NOW  proceed  to  describe  the  chief  features  of  im- 
portance in  the  structure  of  the  shoot  of  the  young  oak- 
plant,  premising  that  many  of  the  remarks  may  here  be 
curtailed  in  view  of  the  facts  already  learned  in  connec- 
tion with  the  root.  The  first  object  will  be  to  bring  out 
the  differences  in  the  shoot  as  contrasted  with  the  root, 
and  first  we  may  examine  the  structure  by  means  of 
transverse  sections  as  before.  The  shoot  consists  of  all 
the  structures  developed  from  the  plumule. 

Such  sections  show  that  we  have  here  also  various 
definitely  grouped  tissues,  of  which  we  may  conveniently 
distinguish  three  systems.  A  series  of  vascular  bundles 
grouped  in  a  close  ring  constitutes  one  of  these  systems ; 
another  is  represented  by  a  single  layer  of  cells  at  the 
periphery  of  the  section,  and  this  is  called  the  epider- 
mis ;  and  the  remainder  of  the  section  composes  the 
third  system,  often  termed  the  fundamental  tissue,  and 
divided  arbitrarily  into  three  regions — the  pith,  the  cor- 
tex, and  the  primary  medullary  rays  (Fig.  9).  The 


40 


THE   OAK. 


chief  points  of  difference  from  the  root  are  that  the 
xylem  and  phloem  of  these  vascular  bundles  of  the  stem 
do  not  alternate  on  the  section,  as  they  did  in  the  root, 
but  the  phloem  of  each  bundle  is  on  the  same  radius  as 
the  xylem  ;  and  that  there  is  no  pericycle,  for  branches 


FIG.  9. — Transverse  sections  through  very  young  twigs  of  oak,  showing 
the  vascular  bundles  of  the  stem  (P  and  X),  arranged  in  a  ring  round 
the  pith,  and  joined  by  the  cambium  ring— the  fine  line  passing 
through  the  bundles ;  M  and  «,  the  vascular  bundles  passing  down 
from  the  leaves — M  the  median  bundles  and  s  the  lateral  bundles. 
The  external  outline  is  the  epidermis ;  the  letters  P  P  stand  in  the 
primary  cortex  ;  the  letters  X  X  stand  in  the  pith ;  the  primary 
medullary  rays  separate  the  bundles.  (After  Mliller.) 

are  not  developed  endogenously  as  rootlets  are.  Then 
there  are  some  important  differences  in  the  mode  of 
origin  of  these  vascular  bundles  in  space.  We  saw  that 
in  the  root  the  first-formed  spiral  vessels  are  developed 
at  the  outer  parts  of  the  axis-cylinder,  nearest  the  cor- 
tex, and  the  succeeding  vessels  are  formed  in  centripetal 
order  from  these  points.  In  the  young  stem  the  exact 


THE  SEEDLING  AND  YOUNG  PLANT.       41 

converse  occurs — the  first  spiral  vessels  arise  near  the 
center  of  the  stem,  and  development  proceeds  centrifu- 
gally  from  the  first.  We  may  begin  our  study  of  the 
shoot  by  tracing  the  course  of  the  vascular  bundles, 
which,  it  must  be  remembered,  are  the  channels  of 
communication  between  the  water-supply  at  the  roots 
below  and  the  leaves  and  young  parts  of  the  shoot 
above. 

If  we  cut  a  transverse  section  of  the  terminal  bud  of 
the  oak,  as  close  to  the  tip  as  possible,  we  shall  obtain  a 
preparation  of  the  young  axis  consisting  entirely  of  em- 
bryonic tissue,  all  the  cells  of  which  are  practically  alike 
— small,  polygonal,  thin-walled  cells,  with  large  nuclei 
and  much  protoplasm,  but  without  sap-vacuoles ;  these 
cells  are  in  a  state  of  active  division,  those  in  the  in- 
terior dividing  successively  in  all  planes.  Those  which 
form  the  peripheral  layer,  however,  are  already  distin- 
guished by  only  dividing  in  the  two  planes  at  right 
angles  to  the  periphery,  and  they  constitute  the  primi- 
tive epidermis.  There  is  no  structure  corresponding  to 
a  root-cap. 

Transverse  sections  a  little  lower  down  show  differ- 
ences of  the  following  nature  :  In  the  first  place,  the 
outline  of  the  section  tends  to  be  somewhat  pentagonal, 
the  points  of  origin  of  the  very  young  leaves  being  at 
the  angles  of  the  pentagon  in  accordance  with  their 
phyllotaxis — i.  e.,  the  order  in  which  the  leaves  are  ar- 
ranged on  the  stem.  This  is  of  such  a  nature  that  each 
leaf  stands  some  distance  above  and  to  one  side  of  its 


42  THE   OAK. 

next  neighbor  below,  and  if  a  line  be  drawn  from  the 
insertion  of  any  one  leaf  through  the  points  of  inser- 
tion of  those  above,  it  will  describe  a  spiral,  and  will 
eventually  come  to  a  leaf  standing  directly  above  the  leaf 
started  from.  In  doing  this  the  spiral  line  will  pass  twice 
round  the  stem,  and  through  the  points  of  insertion  of 
five  leaves.  This  is  shortly  expressed  by  two  fifths. 

The  preyiously  homogeneous  embryonic  tissue  in 
the  section  now  shows  certain  patches  of  grayer,  closer 
tissue,  arranged  round  the  center  in  a  peculiar  manner ; 
these  are  transverse  sections  of  the  young  vascular 
bundles — strands  which  at  present  are  distinguished 
chiefly  by  the  small  diameter  of  their  cells,  whence  the 
darker  gray  appearance. 

These  strands  when  young  are  called  procambium 
strands.  Their  cells  are  distinguished  from  the  other 
embryonic  cells  around  by  growing  more  in  length  and 
dividing  less  frequently  across  their  length,  and  by 
growing  less  in  breadth  and  dividing  more  often  by 
longitudinal  walls. 

On  transverse  sections  a  little  lower  down  there  may 
be  seen  a  number  of  elongated  and  curved  patches  of 
procambium,  as  shown  in  Fig.  9.  On  the  section  it  will 
be  noticed  that  the  larger  strands  are  so  arranged  that 
they  inclose  a  five-angled  mass  of  central  tissue  (the 
pith),  the  five  corners  pointing  to  the  angles  of  the 
young  stem  to  which  the  leaves  are  attached.  At  the 
corners  or  ends  of  the  rays  just  referred  to  are  in  some 
cases  two  or  three  smaller  strands. 


THE  SEEDLING  AND  YOUNG  PLANT.       43 

Now,  the  important  point  to  apprehend  first  is  that 
these  strands  at  the  corners  (M,  s)  are  the  strands  which 
pass  directly  into  the  leaves  through  the  petioles,  and  it 
is  necessary  to  be  perfectly  clear  on  this  subject  in  order 
to  understand  much  of  what  follows.  For  instance,  the 
three  strands  marked  M  in  Fig.  9,  A  (mm,  ms,  and  ms  in 
Fig.  10),  pass  directly  into  a  given  leaf,  m  ?n,  in  the 
middle,  flanked  by  ms  on  either  side ;  but  this  group 
is  also  accompanied  on  each  side  by  another  strand 
(marked  s,  s'  in  Fig.  9,  A,  and  I,  I  in  Fig.  10),  so  that 
five  strands  may  be  regarded  as  contributing  to  each 
corner  of  the  section,  the  three  middle  ones  running 
side  by  side  up  the  midrib  of  the  leaf  and  then 
branching  out  in  a  manner  to  be  described  subse- 
quently. 

It  can  be  shown,  moreover,  that  the  larger  curved 
strands,  occupying  the  sides  of  the  pentagon,  are  simply 
formed  by  the  union  of  several  of  the  smaller  strands  at 
different  levels. 

If,  now,  successively  lower  sections  are  cut  of  the 
very  young  shoot,  and  compared,  or  if  the  shoot  is 
softened  and  dissected,  it  is  possible  to  make  out  the 
course  of  these  vascular  bundle  strands  lower  down ; 
the  course  is  somewhat  complex,  but  the  diagrammatic 
sketches  in  Fig.  11  will  enable  the  reader  to  apprehend 
the  chief  points. 

In  the  first  place,  the  middle  strand  from  a  leaf, 
mm,  passes  vertically  down  in  the  angle  of  the  young 
stem  through  five  internodes  (marked  by  the  horizontal 


44  THE   OAK. 

lines),  turning  to  one  side  and  becoming  continuous  in 
the  fifth  internode  with  a  strand  coming  off  from  an- 
other leaf  situated  at  another  of  the  angles  at  a  differ- 
ent level.  The  strands  which  stand  next  to  this  me- 
dian one— one  on  each  side  (ms) — at  first  also  pass 


ft,  ma"  VMS 

Fio.  10.— Diagram  of  the  course  of  the  bundles  M,  s,  and  s'  of  Fig.  10,  as 
they  pass  out  of  the  stem  into  the  base  of  the  leaf-stalk,  mm  is  the 
median  bundle,  and  ms,  ms  its  two  companions  (M  in  Fig.  9,  A) ;  1,1 
are  the  lateral  bundles  s  and  s'  of  Fig.  9,  A.  The  small  brandies  fst 
go  into  the  stipules.  (After  Frank.) 

vertically  down  together  with  it,  but  at  about  the 
second  or  third  internode  below  they  break  up  into 
smaller  strands,  which  again  join  with  strands  coming 
from  other  leaves  situated  at  other  nodes  and  angles. 

If  we  again  compare  the  figures,  it  will  be  seen  that 
the  three  strands  just  traced  come  down  in  the  angle  of 
the  stem,  only  turning  aside  lower  down — the  median 
strand  mm,  indeed,  running  actually  in  the  angle 
through  five  internodes. 


THE  SEEDLING  AND  YOUNG  PLANT. 


45 


To  right  and  left  in 
Fig.  10  are  seen  two 
strands,  marked  Z,  Z, 
and  these  run  chiefly  in 
what  may  be  called  the 
faces  of  the  five-angled 
stem ;  only,  at  the  node 
where  the  leaf  we  are 
considering  is  inserted, 
they  turn  in  towards 
the  leaf,  and  eventually 
they  run  into  the  sides 
of  the  petiole  of  the  leaf 
as  the  so-called  "  lateral 
strands,"  or  bundles. 

Now,  observation 
shows  that  these  lateral 
strands  (marked  7,  Z2,  Z3, 
etc.,  in  the  diagram, 


FIG.  11.— Diagram  of  the  course 
of  the  vascular  bundles  as 
they  come  down  from  the 
leaves  into  the  stem.  The 
horizontal  dotted  lines  rep- 
resent the  levels  of  sucess- 
ive  leaves ;  the  triangular 
white  area  beneath  the  up- 
per letter  z  is  the  insertion 
of  a  leaf.  Each  group  of 
bundles  form  a  leaf,  as  mm, 
ras,  m?,  etc.  (see  text),  descends  into  the  stem,  and  joins  with  the  bun- 
dles from  other  leaves  after  running  through  several  internodes.  The 
other  letters  refer  to  the  bundles  from  other  leaves.  (After  Frank.) 


46  THE   OAK. 

Fig.  11)  receive  contributions  at  successive  nodes,  and 
pass  down  as  stronger  and  stronger  strands  through 
about  seven  internodes,  their  lower  ends  losing  them- 
selves by  joining  to  others ;  and,  in  fact,  the  larger  bun- 
dles seen  on  the  transverse  section  (Fig.  9)  are  larger 
because  they  consist  of  so  many  contingents  running 
parallel,  or  nearly  so,  down  the  stem. 

It  results  from  this  that  all  the  vascular  bundles  in 
the  stem  are  simply  composed  of  strands  which  run 
into  the  leaves  on  the  one  hand,  and  down  the  inter- 
nodes  on  the  other;  and,  as  further  comparison  will 
show,  all  these  bundles  are  continuous  in  the  stem, 
since  the  lower  ends  of  the  strands  are  joined  on  to 
other  strands. 

Moreover,  as  an  examination  of  the  diagrams  and 
figures  shows,  the  main  course  of  these  bundles  in  the 
stem  is  approximately  parallel — they  run  side  by  side 
down  from  the  leaf  insertion  through  two,  three,  or 
more  internodes,  and  only  bend  aside  to  any  great  ex- 
tent when  they  pass  out  into  a  leaf  or  to  join  with 
others.  In  the  section  (Fig.  9),  for  instance,  all  the 
little  bundles  at  the  angles  and  outside  the  ring  are  cut 
at  levels  where  they  have  abandoned  the  larger  bundles 
and  are  bending  outward  through  the  cortex  to  the 
leaves ;  lower  down  we  should  find  them  joining  to  the 
larger  bundles  at  various  levels,  and  running  down  with 
them,  just  as  strands  from  leaves  at  higher  levels  are 
now  conjoined  to  make  up  these  larger  bundles. 

The  group  of  vascular  bundles  which  passes  into  the 


THE  SEEDLING  AND  YOUNG  PLANT.       47 

stem  from  the  insertion  of  a  leaf  is  spoken  of  collect- 
ively as  the  "  leaf -trace."  Hence  we  see  the  leaf -trace 
of  the  oak  consists  of  five  bundles — one  median,  two 
lateral  median,  and  two  lateral ;  and  since  the  phyllo- 
taxis  of  the  oak  is  two  fifths,  there  will  be  twenty-five 
bundles  in  various  stages  of  separation  or  conjunction 
coming  down  in  the  five  internodes  between  any  one 
leaf  and  the  leaf  vertically  above  it,  as  well  as  the  parts 
of  bundles  from  other  leaves  which  are  still  continuing 
their  course  for  a  short  time. 

Now,  since  the  main  lengths  of  the  course  (in  the 
stem)  of  these  bundles  is  nearly  vertically  downward, 
with  slight  swerves  to  one  side  or  another  as  the  strands 
join,  it  is  obvious  that  on  the  transverse  section  of  the 
stem  the  bundles  will  appear  arranged  in  a  series  round 
the  center — in  fact,  they  will  form  on  the  whole  a  more 
or  less  regular  ring  of  bundles  dividing  off  the  pith  from 
the  cortical  portions  of  the  stem.  Even  in  the  very 
young  condition  (Fig.  9)  we  see  bundles  or  groups  of 
strands  thus  surrounding  the  pith,  only  the  "ring" 
which  they  make  is  a  sinuous  one,  so  that  the  pith  is 
five-rayed — a  characteristic  point  in  the  oak.  At  a 
slightly  later  stage,  as  we  shall  see,  this  ring  of  bundles 
becomes  more  nearly  circular  from  the  gradual  filling 
up  of  irregularities. 

Before  proceeding  further  it  is  necessary  to  make 
clear  one  or  two  other  points.  Since  all  the  vascular 
bundles  in  the  oak-stem  are  bundles  which  are  common 
to  the  stem  and  leaf,  they  are  termed  "  common  bun- 


48  THE   OAK. 

dies."  We  have  seen  that  a  given  strand  or  bundle  may 
run  for  part  of  its  course  simply  side  by  side  with  an- 
other and  separate  from  it ;  at  other  parts  of  the  course 
the  bundles  may  be  united  with  others.  In  the  case  of 
the  oak  it  will  be  clearly  borne  in  mind  that  the  indi- 
vidual or  separate  bundles  of  the  leaf -trace  pass  into  the 
stem  at  the  node  of  insertion  of  the  given  leaf,  and 
then  run  down  side  by  side  at  a  practically  constant 
distance  from  the  surface  of  the  epidermis  on  the  one 
hand,  and  the  longitudinal  axis  of  the  pith  on  the 
other.  At  different  levels  below,  at  or  very  near 
nodes,  these  bundles  turn  aside  laterally — i.  e.,  in  the 
tangential  plane,  and  hence,  still  keeping  their  mean 
distance  from  the  epidermis  and  pith,  join  with 
others. 

This  being  understood,  it  is  also  obvious  that  on  the 
whole  the  collection  of  vascular  bundles  in  a  young 
branch  form  a  nearly  cylindrical  trellis-work  or  mesh- 
work  symmetrically  disposed  between  the  pith  and  the 
cortex,  and  that  the  latter  (cortex  and  pith)  are  in  con- 
nection through  the  meshes  between  the  interpectinat- 
ing  and  concomitant  vascular  bundles.  These  radial 
connections  of  the  pith  and  cortex  are  the  primary 
medullary  rays. 

It  will  now  be  clear  why  we  observe  on  transverse 
sections  of  the  young  stem  taken  across  an  internode 
the  arrangement  shown  in  Fig.  9.  The  vascular  bundles 
are  grouped  in  a  ring  round  the  pith,  separating  it  off 
from  the  cortex  and  its  covering  the  epidermis,  and  with 


THE  SEEDLING  AND  YOUNG  PLANT.       49 

those  primary  medullary  rays  which  happen  to  have 
been  cut  running  between  the  bundles. 

If  we  now  trace  the  vascular  bundles  of  the  leaf- 
trace  in  the  other  direction — that  is,  up  into  the  leaf — 
their  course  is  simple  enough,  as  shown  in  Figs.  10  and 
11.  The  five  bundles  run  through  the  midrib  and  the 
stronger  lateral  ribs  to  the  tips  and  edges  of  the  leaf, 
first  breaking  up  into  several  strands  in  the  petiole  and 
midrib,  and  then  becoming  finer  and  finer  as  they  give 
off  the  lateral  strands.  The  median  bundle  does  little 
more  than  run  directly  through  the  leaf  as  the  midrib, 
becoming  finer  and  finer  as  it  nears  the  apex.  The  two 
lateral  median  bundles  behave  in  a  somewhat  curious 
way.  We  have  already  seen  how  large  and  flat  they  are 
at  the  leaf  insertion  (Fig.  10).  Soon  after  entering  the 
petiole  they  break  up  into  several  strands,  two  of  which 
converge  and  take  a  course  along  the  dorsal  side  of  the 
midrib,  thus  nearly  completing  a  cylinder  of  bundles 
inclosing  a  pith ;  moreover,  the  xylem  portions  of  these 
bundles  are  all  turned  inward  towards  the  pith. 

The  lateral  bundles,  coming  obliquely  into  the  leaf 
insertion,  pass  up  the  midrib  side  by  side  with  the 
above,  and,  like  them,  break  up  into  parallel  strands. 
Before  entering  the  midrib  they  give  off  small  bundles 
(fst  in  Fig.  10)  to  the  pair  of  minute  stipules  which 
flank  the  petiole.  As  the  strands  pass  along  the  mid- 
ribs and  chief  lateral  ribs  they  interosculate  in  various 
degrees,  and  give  off  smaller  side  branches  into  the 
mesophyll  of  the  leaf  (see  Chapter  VI). 


50  THE   OAK. 

The  veins  which  spring  from  the  chief  lateral  ribs 
run  towards  one  another  and  anastomose,  giving  off 
smaller  veins  which  form  a  network  in  the  area  in- 
cluded by  them.  In  the  neighborhood  of  the  leaf- 
margin,  however,  the  smaller  veins  curve  towards  one 
another,  and  make  arches  convex  towards  the  margin. 
In  the  finer  meshes  individual  minute  branches  run  to 
the  center  of  a  mesh  and  end  there.  Eound  the  ex- 
treme edge  of  the  leaf  is  a  single  vascular  bundle ;  this 
receives  small  bundles  from  the  above-mentioned  arches, 
and  also  receives  the  ends  of  the  midrib  and  the  chief 
lateral  ribs  (cf.  Fig.  1). 

The  vascular  bundles  of  the  axillary  bud,  which  will 
eventually,  of  course,  form  a  system  like  that  already 
described  on  their  own  account,  pass  down  and  join  the 
bundles  of  the  parent  axis  as  follows : 

The  bundles  of  each  lateral  half  of  the  bud  (Fig.  11, 
a  a)  pass  down  together  between  the  bundles  of  the 
leaf -trace  of  the  leaf  from  whose  axil  the  bud  arises,  and 
the  next  lateral  bundles  of  the  stem  with  which  the  leaf- 
trace  bundles  are  conjoined ;  the  common  strand  formed 
by  the  bundles  of  each  side  of  the  bud  then  joins  with  a 
bundle  coming  down  from  another  leaf.  A  few  of  the 
strands  may  also  join  to  the  bundles  of  the  leaf-trace 
itself. 

At  the  back  or  top  side  of  the  bud — i.  e.,  the  side 
next  the  stem  which  bears  it — a  few  vascular  bundles 
pass  from  the  bud  to  the  nearest  strand  (Fig.  11,  z) ; 
this  is  the  middle  strand  coming  down  from  the  leaf 


THE  SEEDLING  AND  YOUNG  PLANT.       51 

vertically  above  the  bud — i.  e.,  the  sixth  leaf  up  the 
stem.  Knowing  this,  we  of  course  know  how  the 
branch  is  joined  to  the  stem.  Several  other  small 
strands  also  are  formed,  as  at  z,  to  complete  the  filling 
up  the  gap,  and  these  may  be  called  completing  bun- 
dles. These  connecting  and  completing  bundles  en- 
able the  young  shoot  as  it  develops  from  the  bud  to 
inclose  its  own  pith  in  a  cylinder  of  vascular  tissue  con- 
tinuous with  that  of  the  parent  shoot. 

We  thus  see  that  the  vascular  bundles  form  a  con- 
nected system  in  the  leaves,  buds  (i.  e.,  young  branches), 
and  stem,  and  it  only  remains  to  add  that  they  are 
joined  below  to  those  of  the  root-system,  with  which, 
in  fact,  they  took  origin  in  the  very  young  embryo. 
Hence,  if  we  were  to  remove  the  whole  of  the  softer 
tissues  of  the  oak -plant,  we  should  have  a  model  of  it 
left  in  the  form  of  a  more  or  less  open  basket-work  of 
vascular  bundles.  It  is  necessary  to  bear  this  in  mind, 
as  some  important  conclusions  follow  from  it  subse- 
quently. 


CHAPTER  V. 

THE   SEEDLING   AND   YOUNG   PLANT    (continued}. 

STRUCTURE  OF  THE  VASCULAR  TISSUES,  ETC. 

BEFORE  plunging  into  the  intricacies  of  the  vascu- 
lar bundles  it  will  be  well  to  obtain  some  idea  of  the 
general  plan  of  structure  which  they  present  on  trans- 
verse section  (Fig.  9).  As  already  seen,  each  of  the 
bundles  of  the  ring  consists  of  a  xylem  portion  on  the 
side  next  the  center  of  the  stem,  and  a  phloem  portion 
on  the  side  next  the  periphery,  and  these  portions  are 
separated  by  the  cambium  layer.  The  tissue  in  the 
center  of  the  stem,  and  surrounded  by  the  ring  of  bun- 
dles, is  called  the  pith ;  the  tissue  outside  the  ring,  and 
between  it  and  the  epidermis,  is  called  the  cortex ;  and 
the  tissue  left  between  the  bundles  is  termed  the  pri- 
mary medullary  rays  (Fig.  9). 

It  will,  of  course,  be  remembered  that  the  term 
"  ring,"  as  used  above,  always  expresses  the  fact  that  a 
cylinder  is  here  viewed  in  section.  Now,  the  cambium 
of  the  individual  bundles  soon  unites  across  the  primary 
meflullary  rays,  and  thus  a  complete  hollow  cylinder  of 
cambium  is  formed  throughout  the  stem,  and,  as  we 
shall  see  later,  throughout  the  root  also.  For  the  pres- 


THE  SEEDLING  AND  YOUNG  PLANT.       53 

ent  it  must  suffice  to  notice  that  the  cells  of  this  cam- 
bium cylinder  go  on  developing  into  new  xylem,  or 
phloem,  or  medullary  rays,  according  to  position  and. 
circumstances ;  meanwhile  we  are  only  concerned  with 
the  vascular  bundles  of  the  young  shoot. 

On  the  transverse  section  through  the  very  young 
shoot,  provided  the  preparation  is  thin  and  examined 
with  a  high  power  of  the  microscope,  the  young  vascu- 
lar bundles  are  found  to  present  a  definite  and  symmet- 
rical structure,  easily  distinguished  from  that  of  the 
fundamental  cell-tissue  in  which  they  are,  so  to  speak, 
imbedded  (Fig.  12). 

The  cells  of  the  medullary  rays  are  seen  in  one,  two, 
or  several  rows,  each  cell  having  the  form  of  a  parallelo- 
piped  or  ordinary  brick — the  bricks  being  supposed 
standing  on  their  narrow  sides  and  with  the  long  axes 
directed  radially.  The  walls  in  contact  with  the  vas- 
cular bundles  are  thickened,  and  soon  become  woody 
and  beset  with  simple  pits;  the  cells  contain  proto- 
plasm and  nuclei,  and  in  winter  become  filled  to  crowd- 
ing with  starch  grains.  They  also  contain  tannin. 

The  young  vascular  bundles,  in  section,  project  into 
the  pith — like  wedges  with  a  rounded  point — giving  to 
the  latter  the  five-rayed  shape  on  the  transverse  section 
already  referred  to  (Fig.  9). 

The  cells  of  the  pith  also  have  their  walls  thickened 
and  pitted,  and  also  contain  protoplasm,  nuclei,  and 
tannin,  and  starch  in  winter.  At  the  rounded  angles 
of  the  vascular  wedges  the  cells  are  smaller  than  else- 


THE   OAK. 


Fio  1 '  —Transverse  section  of  young  stem,  showing  primary  vaseukr 
bundles,  etc.,  highly  magnified.  «  and  6,  the  pith  ;  «,  primary  cortex: 
t',  epidermis ;  A,  peridcnn  (cork);  ff,  collcnchyma.  Two  complete 
primary  vascular  bundles,  and  parts  of  two  others,  are  shown,  sepa- 
rated by  the  primary  medullary  rays,  r,  spiral  vessels  (protoxylem); 
t,  bast-fibers  (protophloem) ;  «,  m,  cambium,  separating  the  phloem 
from  the  xylem;  p,  wood-parenchyma.  Secondary  medullary  rays 
urc  seen  in  the  bundles,  as  also  are  pitted  vessels  of  different  sixes. 
(Th-  Hartig.) 


THE  SEEDLING  AND  YOUNG  PLANT.       55 

where  in  the  pith,  but  otherwise  their  shape,  etc.,  are 
similar ;  all  the  pith-cells  are  vertically  twice  or  three 
times  as  long  as  broad.  Thus  the  shape  of  the  cells  is 
that  of  short,  polygonal  prisms,  standing  on  end  and 
closely  packed. 

Imbedded,  as  it  were,  in  the  smaller  pith-cells  at  the 
rounded  angles  of  the  vascular  wedges  are  the  oldest — 
i.  e.,  first-formed — vessels,  looking  like  small  holes  with 
very  firm  outlines  (Fig.  12,  r).  These  are  the  tracheae,  or 
vessels  with  unreliable  spiral  thickenings  on  their  walls. 
From  their  shape  and  peculiarities  they  are  called  spiral 
vessels,  and  from  their  position  and  development  they 
constitute  the  first-formed  elements  of  the  xylem  or 
wood.  They  are  of  very  narrow  caliber,  and  stand  in 
radial,  short  rows,  single  or  branched ;  those  first  devel- 
oped— i.  e.,  nearest  the  pith — are  the  narrowest,  their 
diameter  being  often  even  less  than  that  of  the  smallest 
pith-cells  among  which  they  lie.  As  we  pass  radially 
out  towards  the  cortex  these  vessels  get  wider  and  wider, 
but  the  true  spiral  vessels  are  always  very  narrow  (Fig. 
16,  sp).  Occasionally  some  of  these  vessels  have  annular 
instead  of  spiral  thickenings. 

Of  course,  their  true  characters  are  not  elucidated 
until  we  compare  longitudinal  sections  of  the  stem.  It 
is  then  seen  that  the  spiral  thickenings  are  very  closely 
wound,  sometimes  to  the  right,  sometimes  to  the  left, 
and  occasionally  double.  Comparative  studies  of  longi- 
tudinal sections  also  show  that  these  vessels  at  first  sim- 
ply consist  of  longitudinal  rows  of  very  narrow,  verti- 


56  THE   OAK. 

cally  placed  cylindrical  cells,  standing  end  to  end ;  it  is 
because  the  adjacent  ends  become  resorbed  and  disappear 
that  the  rows  of  cells  at  length  form  long,  continuous 
tubes — vessels,  or  tracheae. 

Turning  once  more  to  the  transverse  section,  as  the 
eye  follows  the  bundle  radially  outward  the  lumina  of 
the  vessels  in  the  radial  rows  are  found  to  become  wider 
and  wider,  until  we  meet  with  vessels  with  diameters 
many  times  greater  than  that  of  the  pith-cells.  The 
walls  of  these  wider  vessels,  however,  are  not  strength- 
ened with  spiral  thickenings,  but  are  thickened  and  fur- 
nished with  bordered  pits,  the  shape  and  characters  of 
which  are  best  seen  from  the  illustrations  (Figs.  14-1 G). 
These  larger  vessels  are  not  always  associated  with  the 
radial  rows  of  spiral  vessels,  but  may  be  scattered  be- 
tween them. 

The  vessels  intermediate  between  the  spiral  and  the 
pitted  ones  are  thickened  sometimes  with  reticulations. 
All  these  larger  vessels  have  septa  inclined  towards  the 
medullary  rays,  and  perforated  with  several  long,  oval, 
parallel,  horizontal  holes  :  hence  the  segments  are  easily 
macerated  and  distinguished,  and  their  lengths  are  found 
to  be  variable  (Fig.  16,  pv). 

The  large  pitted  vessels  form  groups  with  parenchyma 
and  wood-cells  scattered  between,  and  are  confined  chief- 
ly to  the  inner  parts,  forming  radiating  series  side  by 
side ;  in  the  outer  parts  of  the  bundle  are  various  groups 
of  smaller  vessels — the  groups  being  rounded,  or  in  ra- 
dial rows,  or  curved  or  oblique  rows. 


THE  SEEDLING  AND  YOUNG  PLANT. 


57 


58 


THE   OAK. 


THE  SEEDLING  AND  YOUNG  PLANT. 


59 


60  THE   OAK. 

Successive  sections  prove  that  the  vessels  in  the  bun- 
dle change  in  number — i.  e.,  there  are  fewer  when  pass- 
ing from  stem  to  leaf.  A  vessel  may  end  in  an  inter- 
pectinating,  pointed,  terminal  cell;  or  it  may  branch, 
as  it  were,  dichotomously,  owing  to  fusions  with  other 
similar  elements;  or  such  a  fusion  may  occur  lower 
down,  the  original  vessel  ending  blindly. 

In  the  vicinity  of  the  reticulated  and  first  pitted  ves- 
sels, following  on  the  spiral  vessels,  we  find  libriform 
fibers,  tracheids,  wood-parenchyma,  and  secondary  rays 
of  parenchyma ;  the  tracheids  are  especially  in  the  neigh- 
borhood of  the  vessels  (see  Fig.  14). 

The  tracheids  are  long  cells  with  gradually  tapering 
ends,  and  the  walls  rather  thick  but  by  no  means  obscur- 
ing the  lumen ;  on  the  walls  are  numerous,  usually  elon- 
gated, oblique  or  horizontal  bordered  pits.  These  pits 
occur  whether  the  next  element  is  a  tracheid,  a  vessel, 
or  fibers  or  cells  of  any  kind  (Fig.  16,  tr). 

The  length  of  the  tracheids  varies,  and  the  diameter 
is  also  variable. 

The  libriform  fibers  are  also  long  cells,  but  often 
more  pointed  at  the  ends,  and  their  very  thick  walls 
almost  obliterate  the  lumen  (Fig.  16,  /) ;  their  length  is 
about  that  of  the  tracheids,  but  slit-like,  small,  simple 
pits  are  rare  on  their  walls.  In  the  wood  of  later  years, 
however,  the  lengths  may  be  different. 

There  are  also  elements  which  stand  midway  between 
the  true  fibers  and  tracheids ;  they  occur  in  those  parts 
where  masses  of  true  fibers  abut  on  the  groups  consist- 


THE  SEEDLING  AND  YOUNG  PLANT. 


61 


sp. 


f 


p.v. 


FIG.  16. — The  various  chief  elements  of  the  wood  of  the  oak,  isolated  by 
maceration,  and  highly  magnified.  /,  a  fiber,  distinguished  by  its 
thick  vails,  simple  slit-like  pits,  and  no  contents  ;  w..p,  part  of  a  row 
of  wood-parenchyma  cells,  with  simple  pits,  and  containing  starch  in 
winter ;  tr,  a  tracheid,  distinguished  from  the  fiber  especially  by  its 
bordered  pits ;  p.v,  part  of  a  rather  large  pitted  vessel,  made  up  of 
communicating  segments,  each  of  which  corresponds  to  a  tracheid, 
and  has  bordered  pits  on  its  walls ;  sp,  part  of  a  spiral  vessel. 


62  TUB   OAK. 

ing  of  vessels  and  tracheids.  They  resemble  tracheids, 
but  have  very  few  and  small,  scarcely  bordered,  oblique, 
slit-like  pits  :  every  stage  can  be  detected  between  these 
and  true  fibers.  They  must  be  looked  upon  as,  so  to 
speak,  abnormal,  because  their  numbers  are  small  com- 
pared with  the  typical  elements  among  which  they 
occur. 

The  wood-parenchma  consists  of  vertical  groups  of 
short  cells,  each  group  having  the  fusiform  shape  of  a 
tracheid  (Fig.  16,  w.p) :  hence  the  upper  and  lower  cell 
of  each  group  has  a,  pointed  end.  Each  group  obviously 
arises  from  the  transverse  divisions  of  a  long,  prismatic 
cell,  pointed  at  both  ends — a  cambium  cell.  The  trans- 
verse section  is  round,  and  somewhat  larger  than  that  of 
a  tracheid,  and  the  walls  are  somewhat  thinner.  Where 
they  abut  on  vessels  and  tracheids  their  walls  have  bor- 
dered pits,  but  where  they  stand  in  contact  with  similar 
groups,  or  with  parenchyma  rays,  the  pits  are  simple. 
During  periods  of  rest  they  are  loaded  with  starch 
grains. 

The  length  of  the  groups — i.  e.,  of  the  fusiform  cells 
cut  up  into  short  cells — varies;  the  shorter  ones  have 
only  one  transverse  division. 

The  wood-parenchyma  is  less  abundant  than  the  tra- 
cheids and  fibers,  and  predominates  in  the  more  vascular 
parts  ;  after  two  to  four  or  more  fibers  in  a  radial  row  a 
single  parenchyma  cell  may  often  be  seen,  but  other  ar- 
rangements occur.  In  the  parts  where  fewer  vessels  oc- 
cur it  is  not  uncommon  to  find  a  series  of  radial  rows  of 


THE  SEEDLING  AND  YOUNG  PLANT.       63 

about  six  to  ten  fibers  end  in  a  single  parenchyma  cell, 
and  thus  are  formed  short,  tangential  rows  of  wood- 
parenchyma  cells,  intercalated,  as  it  were,  between  the 
radial  rows  of  other  elements  (Fig.  12, p).  It  often  hap- 
pens, moreover,  that  reticulated  and  pitted  vessels  are 
closely  surrounded  by  wood-parenchyma. 

The  secondary  medullary  rays  exist  as  single  radial 
rows  of  cells,  agreeing  in  form,  etc.,  with  the  cells  of 
the  primary  medullary  rays.  In  contact  with  one  an- 
other or  with  wood-parenchyma  their  walls  have  simple 
pits,  but  they  have  bordered  pits  where  they  abut  on 
tracheids  or  vessels.  In  winter  these  cells  are  filled 
with  starch.  On  tangential  sections  (Fig.  15)  it  is  easy 
to  see  how  the  vertical  groups  of  cells  have  the  same 
origin  as  the  groups  of  wood-parenchyma  cells — the 
difference  being  that  the  cambial  cells  which  are  going 
to  be  transformed  by  horizontal  divisions,  etc.,  into  ver- 
tical rows  of  ray  parenchyma,  undergo  repeated  tangen- 
tial longitudinal  divisions,  and  so  continued  radial  rows 
are  formed.  The  cells  of  these  rays  are  often  much 
shorter  than  those  of  the  wood-parenchyma,  yet  all  gra- 
dations occur.  The  mother-cells  may  be  very  long, 
evidently  corresponding  to  two,  and  they  may  also  di- 
vide in  the  radial  longitudinal  plane,  and  the  ray  be- 
come biseriate. 

These  secondary  rays  start  (on  the  transverse  section) 
from  the  first  large  vessels,  or  from  younger  ones,  or  they 
may  start  from  other  points.  The  ray  may  sometimes 
cease  within  the  first  year's  bundle ;  but  the  difficulty 


64  THE  OAK. 

comes  in  of  deciding  whether  a  continuation  occurs  at  a 
higher  or  lower  level. 

The  cells  of  the  cambium,  seen  in  transverse  section, 
are  rectangular  in  shape  and  arranged  in  regular  radial 
rows,  owing  to  the  regular  tangential  divisions  (Fig.  12, 
w,  m).  In  longitudinal  sections  they  are  found  to  be 
like  the  tracheids  in  shape  and  size,  so  that  they  stand 
one  behind  the  other  at  the  same  level.  Regarding  the 
tangential  series  in  rings,  however,  they  are  less  regular, 
because  the  tangential  longitudinal  divisions  of  two  cells 
side  by  side  do  not  lie  in  the  same  tangential  plane. 
This  regular  radial  arrangement  would  be  found  in  the 
xylem  also,  and  is  so  to  a  certain  extent,  but  it  is  dis- 
turbed by  the  differences  in  diameter  which  the  various 
elements  attain  later.  The  fibers  are  most  apt  to  pre- 
serve the  regularity,  but  in  many  cases  growth  in  length, 
and  the  intercalation  of  oblique  septa,  disturb  it. 

In  later  years  the  length  of  the  cambial  cells  in- 
creases, and  hence  the  length  of  the  elements  in  the 
wood. 

The  phloem  or  bast  of  the  individual  bundle  is  sepa- 
rated from  its  neighbors  by  large  rays  of  parenchyma, 
the  cells  of  which  agree  with  the  secondary  bast-paren- 
chyma rays.  As  these  pass  into  the  cortex  they  widen, 
as  they  do  at  the  pith  (Fig.  12). 

The  oldest  portion  of  the  phloem — that  next  the 
cortex — consists  of  a  group  of  thick-walled  bast  fibers 
with  their  lumina  nearly  obliterated;  these  are  long, 
spindle-shaped  fibers  much  like  the  fibers  of  the  wood. 


THE  SEEDLING  AND  YOUNG  PLANT.       65 

As  a  rule,  the  outer  and  inner  side  of  these  bast 
groups  are  in  contact  with  vertical  rows  of  nearly  cubi- 
cal parenchyma  cells,  strongly  thickened  on  the  side  next 
the  bast,  and  each  nearly  filled  with  a  crystalline  clump 
or  with  an  imperfectly  formed  crystal  of  oxalate  of  lime. 
Similar  vertical  rows  of  crystal  cells  may  also  occur 
within  the  groups  of  bast  fibers,  the  walls  of  the  cubical 
cells  being  more  or  less  thickened  and  simply  pitted. 
Occasionally  a  cell  here  and  there  retains  thin  walls. 
The  vertical  rows  result  from  cross-divisions  of  prosen- 
chymatous  mother-cells,  the  conical  ends  being  found  in 
macerations. 

Within  the  groups  of  bast  fibers  are  yet  other  rows, 
similarly  formed,  of  parenchyma  (Fig.  17,  bp),  the  cells 
of  which  are  longer,  however,  attaining  the  length  of 
the  wood-parenchyma;  like  the  latter  also  their  walls 
are  lignified  and  rather  thick,  and  they  contain  starch 
in  the  winter.  Thus  we  have  parenchyma  in  the  bast. 
Transitions  between  these  two  forms  of  parenchyma 
cells  are  also  found. 

The  cells  of  the  rays  between  the  bast  fibers  are 
thickened  and  pitted ;  they  are  rounded,  and  not  in 
vertical  series  as  in  the  rest  of  the  rays,  but  are  scattered 
in  no  particular  order.  Sometimes  they  are  few,  and 
one  or  all  with  very  thick  walls  perforated  by  pit-canals 
(Fig.  17,  bs). 

The  remaining  younger  part  of  the  bast  consists 
chiefly  of  delicate,  apparently  irregular  parenchyma 
cells  with  cellulose  walls;  this  is  easily  traced  to  the 


FIG.  IT.— Transverse  section  of  cortex  and  phlegm  of  oak  (highly  magni- 
fied). £,  the  periderm  (cork),  which  has  replaced  the  epidermis ;  c, 
collenchyma ;  </,  cells  of  cortex  containing  crystals  of  oxalate  of  lime  ; 
«,  schlerenchyma  cells.  All  these  belong  to  the  cortex  proper.  Be- 
low these  come  the  phloem :  5,  J,  groups  of  hard  bast  fibers ;  bp, 
phloem-parenchyma ;  Js,  medullary  ray ;  e,  cells  containing  crystals 
of  oxalate  of  lime.  (Luerssen.) 


TIIE   SEEDLING   AND   YOUNG   PLANT.  67 

cambium.  The  radial  rows  of  the  latter  can  be  followed 
for  some  distance,  the  radial  diameter  of  the  cells  in- 
creasing, the  walls  thickening,  and  the  rectangular  shape 
changing.  Displacements  from  the  radial  arrangement 
then  occur.  A  few  cells  assume  a  nearly  circular  form 
(i.  e.,  in  transverse  section),  and  the  larger  ones  are  ef- 
fective in  causing  displacements.  The  bast  cells  devel- 
oped earlier,  and  therefore  more  distant  from  the  cam- 
bium zone,  now  lie  in  the  perceptibly  large  periphery, 
and  thus  undergo  tangential  extension  or  radial  com- 
pression, and  so  undergo  changes  of  form.  Besides  these 
alterations  in  form  and  position,  the  more  delicate  bast 
elements  increase  in  numbers  by  the  development  of 
perpendicular  division  Avails ;  this  is  quite  clear  in  those 
parts  nearest  the  cambium,  but  farther  out,  where  great 
irregularity  occurs,  it  is  impossible  to  say  which  cells 
have  arisen  direct  from  the  cambium  and  which  by  these 
later  divisions.  Still,  certain  thin  septa  betray  their  late 
origin. 

On  tangential  sections  we  see  elongated,  pointed,  in- 
terpectinating  cells,  with  secondary  rays  of  parenchyma 
between,  showing  that  these  are  formed  and  continued 
by  the  cambium.  Each  pointed  cell  has  proceeded  from 
a  cambium  cell,  and  indeed  only  differs  in  its  thicker 
walls  and  pits.  These  cells  are  still  simple,  or  here  and 
there  have  a  transverse  septum  obliquely  across.  If  the 
tangential  section  is  in  a  slightly  older  portion,  most  of 
the  above  cells  are  found  to  be  septate  and  cut  up  into 
parenchyma-like  cells — irregular  bast-parenchyma.  The 


68  THE   OAK. 

walls,  especially  the  longitudinal  walls,  are  marked  either 
with  crowded  small  pits  giving  a  reticulate  appearance, 
or  have  sieve-plates ;  all  intermediate  stages  occur  also. 
The  transverse  walls  are  also  pitted  with  sieve-plates. 

All  the  cells  of  the  soft  bast  contain  tannin,  and 
small  grains  which  turn  brown  in  iodine  (leucoplasts?). 
Very  little  starch  is  found  in  them  except  in  winter. 
Crystals  occur  in  pitted  cells  here  and  there  (Fig.  18,  d 
and  e). 

Even  in  the  first  year  the  cambium  may  produce 
small  groups  of  thick-walled  bast  fibers  of  exactly  the 
same  character  as  those  of  the  primordial  groups. 

It  is  obvious  that  while  the  wood  elements  remain 
fixed  in  the  cylindrical  surface  where  they  are  developed, 
the  bast  elements  formed  outside  the  cambium,  being 
driven  outward  in  consequence  of  growth  in  thickness, 
come  to  lie  in  a  layer  of  continually  increasing  radius. 
If  these  last  elements  were  unyielding  and  lignified  there 
would  be  a  solid  sheath  of  elements  which  refused  to  ex- 
tend by  mechanical  distention,  cell  division,  or  growth  of 
cell-walls ;  this  would  finally  rupture  under  the  pressure 
from  within.  This  is  prevented  by  the  division  and 
growth  of  the  chief  phloem-elements. 

In  the  vascular-bundle  system  of  the  stem  there  are 
no  essential  differences  in  structure  as  we  pass  from  one 
region  to  another  ;  the  only  variations  are  in  the  thick- 
ness or  breadth  of  the  bundles  at  different  points,  such 
as  where  other  bundles  join  or  leave  them.  As  the  leaf- 
trace  passes  into  the  venation  of  the  leaf  the  ends  be- 


THE  SEEDLING  AND  YOUNG  PLANT. 


69 


come  thinner  (Fig.  21),  and  the  same  is  found  as  it  tails 
off  below ;  changes  in  structure  also  appear  in  the  leaves. 


FIG.  18. — Longitudinal  radial  section  of  the  cortex  and  phloem  of  oak. 
References  as  in  Fig.  17.    (Luerssen.) 

The  first  noticeable  change   is   the  diminution   in 
the  number  of  wood  fibers  and  the  presence  of  narrow 


70  THE   OAK. 

vessels  only.  As  the  trace  passes  through  the  cortex  to 
the  leaf  the  actual  number  of  both  xylem-  and  phloem- 
elements  diminishes ;  hence  it  comes  about  that  the 
bundles  in  the  leaves  consist  to  a  relatively  large  extent 
of  spiral  vessels  in  the  xylem  and  of  sieve-tubes  in  the 
phloem.  As  the  bundles  leave  the  midrib  and  larger 
veins  the  true  continuous  vessels  disappear  altogether, 
and  only  spindle-shaped  tracheids  with  reticulated  or 
spiral  thickenings  occur,  fitting  obliquely  at  their  point- 
ed ends,  and  which  are  shorter  and  shorter  as  we  ap- 
proach the  ends  of  the  bundles. 

The  phloem  also  is  at  length  reduced  to  little  more 
than  one  or  two  sieve-tubes,  the  segments  of  which  are 
shorter  and  shorter  as  we  near  the  end.  The  shorten- 
ing of  the  elements  is  in  evident  correlation  with  the 
early  cessation  of  growth  in  length  of  the  parts  of  the 
leaf,  and  the  diminution  of  the  number  of  elements 
with  the  decreased  supply  of  fluids,  etc.,  on  the  one 
hand,  and  the  smaller  weight  and  strains  to  be  sup- 
ported on  the  other. 

We  may  sum  up  the  changes  in  structure  towards 
the  ends  of  the  vascular  bundles  thus  :  The  thickening 
of  the  walls  is  less,  and  the  elements  become  narrower 
and  shorter ;  the  xylem  becomes  simplified  by  the  loss 
of  fibers  and  vessels,  until  finally  only  delicate  tracheids 
are  left  (Fig.  21),  the  thickenings  of  which  are  at  length 
not  spirals  or  nets  for  the  most  part,  but  irregular  pit- 
tings.  Moreover,  they  are  nearly  isolated.  Neverthe- 
less, the  inner  elements  can  be  distinguished  as  primary 


THE  SEEDLING  AND  YOUNG  PLANT.       71 

tracheal  elements,  because,  being  earlier  formed,  they 
partook  more  in  what  elongation  occurred,  and  their 
spirals,  for  instance,  are  wider  apart. 

In  the  midrib,  in  proportion  as  the  structural 
changes  go  on,  the  bundles  approach  one  another,  the 
separating  parenchyma  becoming  narrower  and  nar- 
rower. The  pith  consists  of  parenchyma,  chiefly  un- 
lignified  and  with  simple  pits,  but  as  the  bundles  are 
approached  the  cells  become  longer  and  lignified ;  the 
rays  between  the  xylem  groups  are  also  lignified. 

Towards  autumn  the  cells  of  the  pith  and  rays  fill 
with  starch ;  this  is  nearly,  but  not  quite,  all  resorbed 
before  the  leaf  falls. 

The  termination  of  the  bundles  in  the  leaf  consists 
only  of  a  few  narrow  spiral  and  reticulated  cells,  which 
at  last  become  very  short  and  variable  in  shape,  and  of 
a  few  small  sieve  elements  and  cells  (see  Chapter  VI). 


CHAPTER  VI. 

THE   SEEDLING   AND   YOUNG    PLANT  (continued). 

THE  BUDS  AND  LEAVES. 

THE  buds  of  the  oak — those  in  the  leaf -axils  as  well 
as  those  at  the  tips  of  the  young  shoots — are  character- 
istically short  and  broad  ovoid  bodies,  consisting  of 
numerous  overlapping  brown  scales  covered  with  short, 
silky  hairs,  especially  at  the  margins  (Fig.  19).  These 
scales  are  really  the  stipules  of  arrested  leaves,  as  is 
shown  by  the  proper  leaf -blades  being  developed  as  well 
under  certain  circumstances,  such  as  when  nutritive  ma- 
terials are  directed  to  the  young  buds.  The  same  mor- 
phological fact  is  also  shown  by  the  position  of  the  in- 
florescences and  young  leaves  higher  up  in  the  bud,  for 
they  spring  from  between  the  scales,  and  not  from  their 
axils  proper  (see  Fig.  32).  It  is  of  the  highest  impor- 
tance to  understand  that  a  bud  is  simply  the  young 
state  of  a  shoot,  and  that  it  consists  of  the  growing- 
point  of  the  shoot  enveloped  by  closely-folded  leaf 
structures.  In  the  oak  the  buds  are  already  formed 
before  the  end  of  June,  and  on  looking  closely  into  the 
axils  of  the  leaves  on  the  young  shoots — which  have  by 


THE   SEEDLING  AND  YOUNG  PLANT.  73 

that  time  ceased  to  elongate  to  any  considerable  extent 
farther — they  may  be  seen  as  small,  green,  hairy  bodies. 
During  the  remainder  of  the  summer  the  chief  changes 
going  on  in  these  buds  is  a  slow  swelling,  due  to  the 


FIG.  19. — A.  End  of  a  branch  of  oak  showing  the  characteristic  winter 
buds.  B.  A  group  of  buds  (slightly  magnified) :  a,  bud-scales ;  d, 
leaf-scars.  C.  The  same,  in  longitudinal  section  :  a,  bud-scales  (stip- 
ules); &,  young  leaves;  c,  vascular  bundles;  rf,  leaf-scars.  (Prantl 
and  Hartig.) 

gradual  storing  up  of  nutritive  materials  in  the  pith 
and  growing-point  and  to  the  slow  division  of  the  cells. 
A  vertical  section  through  the  bud  at  the  end  of  the 
autumn  shows  the  following  structures  (Fig.  19,  c)  :  A 
conical  growing-point,  consisting  of  embryonic  tissue, 


74  THE   OAK. 

occupies  the  center;  around  this,  arranged  in  a  close 
spiral,  are  several  young  rudiments  of  foliage  leaves, 
each  consisting  of  meristem,  the  cells  of  which  are 
undergoing  divisions.  The  youngest  leaf  is  next  the 
apex  of  the  cone — i.  e.,  the  order  of  development  is 
acropetal — and  each  is  folded  with  the  upper  surfaces 
of  each  half  in  contact ;  two  extremely  minute  stipules 
accompany  each  leaf.  Lower  down  on  the  cone  come 
the  numerous  (about  thirty)  overlapping  scales,  and  be- 
tween several  pairs  of  the  upper  of  these  the  male  in- 
florescences develop.  The  female  inflorescences  are 
developed  in  the  axils  of  two  or  three  of  the  above- 
described  true  leaves  in  a  terminal  bud ;  they  are  not 
normally  formed  in  the  lateral  buds  of  the  shoot  (see 
Chapter  IX). 

All  the  leaves  of  the  shoot  may  have  such  buds 
formed  in  their  axils  during  the  summer,  but  only  some 
of  them  develop  in  the  following  spring ;  it  is  the  buds 
in  the  axils  of  the  lower  leaves  of  the  shoot  which 
usually  come  to  nothing. 

The  normal  course  of  events  is  that  the  bud-scales 
(stipules)  become  dry,  and  the  protected  growing-point, 
with  its  rudimentary  leaves  and  flowers,  passes  into  a 
dormant  condition  lasting  through  the  winter;  but  it 
is  a  very  common  event,  especially  in  a  wet  autumn 
following  a  dry,  hot  summer,  to  find  the  winter  buds 
beginning  to  shoot  out  in  August,  and  not  passing  into 
the  prolonged  state  of  dormancy.  Such  shoots  are 
known  as  Lammas  shoots.  In  some  districts  the  oak 


THE  SEEDLING  AND  YOUNG  PLANT.  75 

forms  numbers  of  these  Lammas  shoots  every  year,  and 
the  tendency  to  produce  them  seems  to  be  capable  of 
being  inherited. 

The  process  of  sprouting,  or  putting  forth  the  shoot 
from  the  bud,  is  the  same  in  all  the  cases.  As  the  tem- 
perature and  other  conditions  improve  in  the  spring,  for 
instance,  the  process  of  cell-division  in  the  growing- 
point  (and  its  derivatives,  the  young  leaves,  etc.)  goes 
on  rapidly,  and  the  stores  of  nourishment  already  there 
and  in  the  pith  and  other  tissues  close  at  hand  are  used 
up.  This  originates  a  series  of  currents  of  food  materi- 
als setting  slowly  towards  these  centers  of  consumption 
from  other  parts  of  the  tree,  and  very  soon  the  numer- 
ous cells  developed  begin  to  absorb  water  with  relatively 
enormous  rapidity  and  vigor.  This  brings  about  two 
chief  changes — the  rapid  elongation  of  the  parts  of  the 
cone  situated  between  the  points  of  insertion  of  suc- 
cessive leaves  (i.  e.,  the  internodes),  and  the  almost  si- 
multaneous expansion  of  the  hitherto  small  and  folded 
leaves.  Thus  the  rapid  extension  of  the  shoot  is  due 
almost  entirely  to  the  energetic  absorption  of  water  into 
cells  for  the  most  part  already  in  existence.  The  chief 
changes  which  follow  consist  in  the  perfection  of  the 
structures — the  development  and  thickening  of  vascular 
tissues,  cell-walls,  etc. 

This  process  of  rapid  extension  does  not  occur  in  the 
internodes  between  the  bud-scales,  or,  at  any  rate,  to  a 
slight  degree  only,  just  sufficient  to  enable  the  shoot  to 
throw  the  scales  off;  hence  the  base  of  the  outgrown 


76  THE   OAK. 

shoot  shows  a  number  of  small  scars  in  a  close  spiral. 
These  scars  of  the  stipular  bud-scales,  like  those  of 
fallen  leaves,  exhibit  the  points  of  rupture  of  the  vascular 
bundles  which  ran  across  from  the  bundles  of  the  bud- 
axis.  It  only  remains  to  point  out  that  the  buds  vary 
in  size  and  vigor  according  to  the  age  and  condition  of 
the  tree ;  the  buds  on  oaks  less  than  fifty  years  old  very 
rarely  have  inflorescences  developed  in  them,  and  I 
shall  defer  the  consideration  of  these  till  we  come  to 
the  flower. 

The  mature  leaf  of  the  oak  (Fig.  20)  is  obovate  in 
general  outline,  with  rather  deep  sinuses  cutting  the 
margin  on  each  side  into  about  six  or  eight  rounded 
lobes ;  the  apex  is  rounded  or  blunt,  and  some  variation 
occurs  in  the  degree  of  incision  between  the  lobes.  The 
base  either  tapers  slightly  into  an  evident  petiole,  or  it 
is  prolonged  on  either  side  of  a  very  short  petiole  so  as 
to  form  small  auricles.  In  the  commonest  variety  the 
margins  and  surfaces  of  the  leaf  are  quite  smooth,  but 
the  raceform  known  as  Quercus  sessiliflora  has  the 
young  leaves  pubescent  beneath. 

The  venation  consists  of  a  midrib  running  from  base 
to  apex,  and  pinnate  lateral  ribs  running  from  the  mid- 
rib at  an  angle  of  about  forty-five  degrees  to  the  tip  of 
each  lobe,  the  points  of  origin  being  alternate  or  nearly 
opposite,  and  the  angle  referred  to  subtending  forward. 
These  principal  ribs  are  prominent  below,  but  not  at  all 
so  above.  The  leaf -tissue  (mesophyll)  between  these  is 
permeated  by  numerous  smaller  vascular  bundles  united 


THE   SEEDLING   AND   YOUXG  PLANT 


77 


into  an  irregular  network,  but  so  arranged  that  they 
leave  between  them  nearly  equal  small  areas  not  trav- 
ersed by  bundles. 


FIG.  20.— Sprigs  of  oak,  showing  the  habit  and  the  arrangement  of  the 
acorns,  etc.,  in  September.    (After  Kotschy.) 


78 


THE   OAK. 


When  young,  the  leaves  are  red,  gradually  becoming 
a  bright  apple-green,  and  finally — in  the  autumn — be- 
coming russet-brown  in  color.  Young  oaks  retain  their 
dead  leaves  till  far  into  the  winter,  and  even  old  trees 
usually  have  some  leaves  attached  till  January.  The 
young  leaves  secrete  small  quantities  of  sweet  liquid  on 

the  superior  face  of 
the  lamina,  and  are 
much  visited  by  bees 
and  wasps ;  this  honey 
must  come  through 
the  membrane.  As  the 
leaves  approach  ma- 
turity the  lamina  be- 
comes bright  and 
hard. 

The  arrangement  of 
the  leaves  is  expressed 
by  the  fraction  two 
fifths,  as  already  de- 
scribed, each  node  giv- 
ing off  one  leaf  at  an 
open  angle,  the  points 
of  insertion  being  so  arranged  that  a  line  drawn  from  the 
insertion  of  a  given  lower  leaf,  and  joining  it  to  the  points 
of  insertion  of  those  above,  passes  twice  round  the  twig 
before  we  arrive  at  the  leaf  situated  vertically  above  the 
one  started  from,  and  this  upper  leaf  is  the  sixth  above. 
Although  this  is  the  commonest  and  normal  arrange- 


FIG.  21. — A  portion  of  the  ultimate  rami- 
fications of  the  vascular  bundles,  show- 
ing tracheids  only,  isolated  from  the 
leaf  by  maceration. 


THE  SEEDLING  AND  YOUNG  PLANT.  79 

ment,  however,  other  dispositions  are  occasionally  met 
with  on  the  same  plant.  The  young  leaves  are  folded 
in  the  bud  in  such  a  manner  that  the  two  halves  of  the 
lamina  lie  one  on  the  other,  the  upper  surfaces  heing 
in  contact  (conduplicate  vernation),  the  margins  being 
therefore  turned  upward. 

In  order  to  understand  the  structure  of  the  leaf,  let 
us  look  at  a  section  cut  neatly  across  the  midrib  and 
lamina,  and  examined  with  the  microscope.  It  is  found 
to  consist  of  three  principal  parts — an  epidermis  above 
and  below,  and  all  round  the  margins,  and  therefore 
over  the  whole  of  the  leaf ;  this  epidermis  is,  in  fact,  a 
continuation  of  that  of  the  young  shoot-axis,  and  envel- 
ops the  whole  of  the  remaining  leaf-tissues.  Inside  this 
we  have  the  main  mass  of  the  leaf  substance — called  the 
mesophyll — consisting  of  thin-walled  cells  arranged  in 
a  peculiar  manner,  and  containing  (in  addition  to  less 
obvious  structures)  large  numbers  of  green  chlorophyll 
corpuscles ;  it  is  the  predominance  of  these  corpuscles 
which  causes  the  leaves  to  appear  uniformly  green. 
Here  and  there  we  see  vascular  bundles,  imbedded,  as  it 
were,  in  the  mesophyll,  cut  across  in  various  directions ; 
and  when  it  is  remembered  that  these  vascular  bundles 
constitute  the  venation  of  the  leaf,  this  phenomenon  is 
easily  explained. 

As  we  have  already  seen,  the  vascular  bundles  of  the 
venation  (Fig.  20)  are  simply  the  much-branched  and 
thinned-off  upper  ends  of  the  vascular  bundles  from  the 
shoot-axis,  the  lower  ends  of  which  join  the  vascular  sys- 


80 


THE  OAK. 


tern  of  the  latter  lower  down.  Now  the  next  point  to  be 
clearly  apprehended  is  that  these  vascular  bundles  of  the 
leaves  have  the  double  duty  of  supporting  the  flattened 


FIG.  22. — Sections  across  the  leaf  of  oak.  A.  Slightly  magnified  and 
semi-diagrammatic,  to  show  the  general  arrangement  of  the  prin- 
cipal vascular  bundles  as  seen  cut  across:  m,  midrib:  «,  marginal 
veins ;  s,  lateral  branches  of  midrib.  Other  smaller  veins  scattered 
oetween.  B.  A  highly  magnified  vertical  section  of  part  of  the 
above  at  a  place  free  from  vascular  bundles :  «,  upper  epidermis,  with 
cuticle,  c;  />,  palisade  cells;  cA,  chlorophyll  corpuscles,  only  drawn 
in  a  few  cells;  m,  spongy  tissue  of  mesophyll;  «.s,  intercellular  pas- 
s-ages communicating  with  the  stoma,  st,  in  the  lower  epidermis,  I. 

mass  of  leaf -tissue,  and  of  carrying  to  and  from  its  cells 
the  water  from  the  roots  and  the  organic  substances 


THE  SEEDLING  AND  YOUNG  PLANT.       81 

formed  in  the  cells  of  the  leaves.  The  water,  with  salts 
in  solution,  coming  from  the  soil  after  it  has  been  ab- 
sorbed by  the  root-hairs,  passes  up  the  wood  (xylem)  of 
the  roots  and  stem,  through  the  vessels  of  the  petioles 
and  leaf -venation,  and  is  finally  distributed  to  the  cells 
of  the  mesophyll ;  the  substances  formed  in  these  cells 
then  pass  down  by  the  phloem  (sieve-tubes,  etc.)  of  the 
venation  and  leaf -stalk,  and  thence  are  distributed  to 
other  parts  of  the  plant. 

Now  let  us  look  at  the  mesophyll  which  these  vascu- 
lar bundles  support  and  serve  as  conduits  for.  It  con- 
sists of  two  distinct  parts  (Fig.  22).  Beneath  the  upper 
epidermis,  the  cells  of  which  are  fitted  closely  together 
without  intercellular  spaces  and  are  devoid  of  chlorophyll 
corpuscles,  there  are  one  or  two  rows  of  vertical  sausage- 
shaped  cells,  closely  arranged  like  the  wooden  railings 
of  a  complete  palisade — consequently  they  are  termed 
the  palisade  cells.  The  lower  moiety  of  the  mesophyll, 
on  the  other  hand,  is  composed  of  irregular  cells  with 
large  intercellular  spaces  between  them,  and  this  loose, 
spongy  tissue,  as  it  is  aptly  called,  abuts  below  on  the 
lower  epidermis.  Both  the  palisade  cells  and  those  of 
the  spongy  tissue  contain  numerous  chlorophyll  cor- 
puscles, as  said. 

This  lower  epidermis  is  worth  a  few  minutes'  con- 
sideration. It,  like  the  upper  epidermis,  is  also  com- 
posed chiefly  of  closely  fitting  cells  devoid  of  chlorophyll 
corpuscles,  excepting  that  here  and  there  we  notice  pairs 
of  smaller  cells  containing  chlorophyll — each  pair  with 


82  THE  OAK. 

a  minute  gap  between  them,  and  the  gap  communicates 
with  the  intercellular  air-cavities  between  the  cells  of 
the  spongy  mesophyll  (Fig.  22,  st).  If  we  remove  a 
piece  of  this  epidermis,  and  look  at  it  as  laid  flat  (in- 
stead of  in  section)  under  the  microscope,  we  find  that 
these  pairs  of  small  cells  are  shaped  somewhat  like  a 
small  mouth,  the  two  curved  lips  of  which  are  formed 
by  the  two  cells  just  mentioned,  and  the  orifice  of  which 
is  the  gap  just  referred  to  (Fig.  23).  These  two  lips  are 
called  the  guard-cells,  and  the  whole  apparatus  is  termed 
a  stoma.  It  is  necessary  to  realize  two  great  facts  about 
these  stomata  on  the  under  surface  of  the  leaf :  firstly, 
there  are  several  hundreds  of  thousands  of  them  on  an 
oak-leaf,  each  square  millimetre  having  from  300  to  350 
of  them  scattered  over  it ;  and,  secondly,  each  one  can 
open  or  close  its  little  aperture  by  the  approximation 
or  divarication  of  the  inner  concave  sides  of  the  curved 
guard-cells. 

If  this  is  clear,  it  will  be  readily  understood  that 
these  stomata  can  regulate  the  amount  of  water  passing 
off  by  evaporation  from  the  walls  of  the  millions  of 
cells  of  the  mesophyll,  especially  if  the  further  fact  is 
borne  in  mind  that  water-vapor  scarcely  passes  at  all 
through  the  close-fitting  epidermis  cells  themselves. 

"We  are  now  in  a  position  to  form  a  sort  of  picture 
of  the  mechanism  of  the  shoot  and  root  in  regard  to 
this  matter.  The  root-hairs  absorb  water  from  the  soil, 
and  in  this  water  there  are  dissolved  small  quantities  of 
the  soluble  salts  of  the  earth — chiefly  sulphates,  nitrates, 


THE  SEEDLING  AND  YOUNG  PLANT.       83 

and  phosphates  of  lime,  magnesia,  and  potash— just  as 
there  are  in  ordinary  well-water.  This  extremely  dilute 
solution  passes  into  the  root-fibers  and  up  through  the 


FIG.  23.— A.  A  small  piece  of  the  lower  epidermis  removed  (and  highly 
magnified)  to  show  the  stomata,  g ;  A,  minute  hairs.  The  guard-cells 
contain  chlorophyll  corpuscles,  whereas  the  ordinary  epidermal  cells 
do  not.  B.  A  stoma  in  vertical  median  section,  cut  across  its  longer 
axis :  a,  intercellular  space :  g,  guard-cell  with  chlorophyll  corpuscles ; 
«,  orifice  of  stoina. 

vessels,  etc.,  of  the  vascular  bundles  of  the  roots,  collect- 
ing into  the  larger  and  larger  channels  until  it  reaches 


84  THE  OAK. 

the  stem ;  here  it  passes  up  the  xylem  to  the  branches, 
petioles,  and  leaf-venation — always  in  the  wood — and 
is  finally  distributed  to  the  mesophyll  cells,  which  ab- 
sorb it  and  evaporate  the  greater  part  of  the  water  into 
the  intercellular  passages  communicating  with  the  outer 
air  through  the  stomata. 

Two  points  need  notice  here.  The  first  is  that  this 
absorption  and  evaporation  in  the  mesophyll  constitute 
a  cause  of  the  upward  movement  of  the  water  in  the 
vascular  bundles — a  movement  which  is  propagated 
through  the  whole  stem  until  it  makes  itself  effective 
even  in  the  roots.  The  exact  mechanism  of  the  move- 
ment in  the  stem  itself  is  too  complex  for  discussion 
here ;  but  I  may  sum  up  the  matter  by  saying  that  the 
disappearance  of  the  water  at  the  surfaces  of  the  leaves 
starts  a  series  of  flows  in  directions  of  least  resistance 
towards  the  mesophyll,  and  as  long  as  the  evaporation 
goes  on  more  water  flows  into  the  cells,  to  replace  that 
lost,  from  the  vessels  of  the  stem,  when  the  water- 
columns  are  supported  and  moved  partly  by  capillarity 
and  by  the  air-bubbles  in  the  cavities,  and  partly  by  a 
peculiar  co-operation  of  the  living  cells  of  the  medullary 
rays.  The  second  point  referred  to  above  is  that  the 
evaporation  from  the  mesophyll  cells  will  be  the  more 
rapid  in  proportion  as  the  air  outside  is  drier  and  the 
stomata  wide  open ;  and  the  more  energetic  this  evap- 
oration is,  the  more  salts  the  mesophyll  cells  will  ac- 
quire in  a  given  time,  because,  of  course,  the  salts  do 
not  pass  away  in  the  evaporated  water  but  are  left  in 


THE  SEEDLING  AND  TOUNG  PLANT.       85 

the  cells.  It  has  been  calculated  that  an  oak-tree  may 
have  700,000  leaves,  and  that  111,225  kilogrammes  of 
water  may  pass  off  from  its  surface  in  the  five  months 
from  June  to  October,  and  that  226  times  its  own 
weight  of  water  may  pass  through  it  in  a  year. 

Now  comes  the  question,  What  are  the  salts  needed 
for  that  so  much  mechanism  should  be  expended  on 
their  accumulation  ?  To  answer  this,  we  must  look  at 
the  mesophyll  cells  a  little  more  closely. 

Each  of  these  consists  of  a  thin  cellulose  cell-wall, 
lined  with  colorless  protoplasm,  which  incloses  a  large 
sap-cavity  (vacuole) ;  in  the  protoplasm  are  imbedded  a 
number  of  bright-green,  rounded  chlorophyll  corpuscles, 
a  relatively  large  nucleus,  and  a  few  less  conspicuous 
granules,  etc.  The  cell-sap  contains  various  substances 
dissolved  in  water.  Some  of  these  substances  are  salts 
arfd  other  materials  ready  to  be  made  use  of ;  others  are, 
so  to  speak,  waste  products  or  worked-up  materials  that 
are  going  to  be  got  rid  of,  or  sent  to  places  where  they 
will  be  made  use  of,  respectively. 

In  the  colorless  protoplasm  which  lines  the  interior 
of  the  cell-wall  and  surrounds  the  cell-sap  we  find  a 
nucleus  and  the  chlorophyll  corpuscles,  as  said,  and  a 
few  words  must  be  devoted  to  the  latter.  Each  chloro- 
phyll corpuscle  consists  of  a  rounded  mass  of  proto- 
plasmic substance  of  somewhat  spongy  texture,  contain- 
ing the  peculiar  green  body,  chlorophyll,  imbedded  in 
it  as  in  a  matrix.  These  chlorophyll  corpuscles  are  liv- 
ing organs,  and  they  require  food  materials — water,  oxy- 


86  THE   OAK. 

gen,  etc. — for  the  support  of  their  life  processes,  just  as 
do  the  other  living  parts  of  the  cell — e.  g.,  the  colorless 
protoplasm  and  nucleus.  They  obtain  these  from  the 
cell-sap,  through  the  agency  of  the  colorless  protoplasm 
in  which  they  reside. 

In  order  that  they  may  perform  their  functions  prop- 
erly, however,  it  is  essential  that  they  be  exposed  to 
light ;  this  is  effected  by  their  being  in  cells  which  are 
disposed  in  thin  layers,  such  as  we  have  seen  the  meso- 
phyll  of  the  leaf  to  be.  In  fact,  the  flat,  thin,  expanded 
form  of  the  leaf  is  a  direct  adaptation  to  the  end  that 
these  chlorophyll  corpuscles  shall  be  properly  illumi- 
nated by  the  sunlight ;  moreover,  the  large  intercellular 
passages  which  communicate  by  thousands  of  stomata 
with  the  atmosphere  insure  their  being  thoroughly 
aerated.  In  addition  to  allowing  the  free  access  of  the 
oxygen  of  the  air,  moreover,  these  intercellular  passages 
admit  of  the  small  quantities  of  carbon  dioxide  in  the 
atmosphere  also  reaching  the  chlorophyll  corpuscles. 
Oxygen  and  carbon  dioxide,  therefore,  are  found  dis- 
solved with  the  other  materials  in  the  cell-sap  which 
saturates  the  protoplasm  and  reaches  the  chlorophyll 
corpuscles. 

These  facts  premised,  we  are  in  a  position  to  follow 
generally  the  astounding  transformations  which  go  on 
in  these  millions  of  chlorophyll  corpuscles  in  the  oak- 
leaf.  Carbon  dioxide  and  water  exist  side  by  side  in  the 
protoplasm  of  the  chlorophyll  corpuscle,  and  rays  of  sun- 
light— i.  e.,  energetic  vibrations  of  the  ether  which  per- 


THE  SEEDLING  AND  YOUNG  PLANT.  87 

vades  the  universe — penetrate  into  the  system.  By 
means  of  the  energy  thus  derived  from  the  sun,  the 
molecules  of  carbon  dioxide  and  water  are  broken  up  in 
the  meshes  of  this  chlorophyll  corpuscle,  and  experi- 
ments prove  that  the  chlorophyll  substance  plays  the 
part  of  the  "trap  to  catch  a  sunbeam."  We  are  not 
concerned  with  the  hypothetical  explanations  offered  for 
all  the  details  of  this  remarkable  process,  but  the  pres- 
ent position  of  science  enables  us  to  say  that,  be  these 
what  they  may,  the  chlorophyll  corpuscle  gains  energy 
from  the  sun,  and  brings  this  energy  to  bear  on  the  car- 
bon dioxide  and  water  in  such  a  way  that  it  does  work 
in  tearing  asunder  their  molecules  in  the  substance  of 
the  corpuscle.  Then  a  curious  series  of  results  follow. 
The  carbon,  oxygen,  and  hydrogen  undergo  new  re-ar- 
rangements, which  amount  finally  to  this — the  substance 
known  as  starch,  and  consisting  of  carbon,  hydrogen, 
and  oxygen,  is  built  up  in  the  form  of  granules  in  the 
chlorophyll  corpuscle,  and  the  surplus  oxygen  escapes 
into  the  sap  and  finds  its  way  to  the  intercellular  pas- 
sages, and  thence  through  the  stomata  into  the  atmos- 
phere. 

It  will  be  obvious  from  the  foregoing  that  the  gran- 
ules of  starch  represent  so  much  matter  (especially  car- 
bon) obtained  from  the  atmosphere  outside  the  plant, 
and  so  much  energy  obtained  from  the  sun ;  each  gran- 
ule may  therefore  be  regarded  as  a  packet  of  stored 
energy  and  matter  won  from  the  external  universe. 

The  limits  of  this  little  book  will  not  allow  of  my 


88  THE   OAK. 

going  into  details  concerning  the  use  which  the  plant 
makes  of  this  starch,  and  it  must  suffice  to  say  that  the 
starch  serves  as  the  basis  of  all  the  constructive  materi- 
als used  by  the  tree.  Thus  it  is  converted  into  a  soluble 
form,  and  combined  with  nitrogen,  phosphorus,  sulphur, 
etc.  (obtained  from  the  earth-salts),  to  make  new  proto- 
plasmic materials,  and  it  passes  down  from  the  leaves  to 
nourish  all  the  living  cells  that  require  it,  in  the  embry- 
onic tissue  at  the  apex  of  the  roots,  and  that  at  the  apex 
of  the  stem  and  branches,  buds,  etc.,  and  some  of  it 
passes  to  nourish  the  cambium  cells,  the  developing  flow- 
ers, acorns,  etc. ;  in  short,  wherever  new  organic  ma- 
terial is  needed  it  is  supplied  from  these  stores  formed 
by  the  green  leaves  waving  in  the  sunshine.  If  we 
reflect  that  the  little  embryo  in  the  acorn  starts  its  life 
with  only  a  minute  store  of  starch  and  proteids  in  its 
cotyledon,  and  that  all  the  tons  of  organic  material 
(chiefly  wood)  found  in  an  old  oak-tree  have  been  super- 
added  to  this  by  the  action  of  the  leaves — the  small  pro- 
portion of  salts  taken  up  by  the  roots  being  quite  incon- 
siderable in  comparison — we  obtain  some  idea  of  the 
enormous  gain  of  matter  and  energy  from  the  outside 
universe  which  goes  on  each  summer. 


• 


CHAPTER  VII. 

THE   TKEE — ITS    BOOT-SYSTEM. 

WE  may  now  suppose  the  young  oak-plant  to  be 
rapidly  developing  into  a  tree.  Technically  the  seedling 
is  said  to  be  a  plant  after  the  first  year,  and  when  it 
reaches  the  height  of  a  few  feet  the  young  tree  is  called 
a  sapling;  these  ideas  are  by  no  means  well  defined, 
however,  and  we  may  regard  them  as  arbitrary  terms  of 
little  or  no  scientific  value. 

The  principal  changes  which  are  noticeable  as  the 
little  tree  grows  larger  are  the  gradual  increase  in  the 
length  and  thickness  of  the  stem,  and  in  the  number 
and  spread  of  the  branches  put  forth  year  after  year. 
Corresponding  with  these  increments,  each  spring  sees  a 
greater  number  of  leaves  than  the  one  before,  and  it  is 
easy  to  prove  that  the  roots  also  become  more  numerous 
and  complex  each  season. 

The  above  simply  expresses  certain  facts  of  observa- 
tion, but  it  is  more  accurate  to  link  them  together  as 
follows : 

In  each  successive  season  of  growth  the  young  oak 
develops  more  leaves  than  it  did  before — in  other  words, 
the  total  area  of  the  leaf -surface  exposed  to  the  air  and 


90  THE  OAK. 

sunlight  is  larger  each  successive  summer  than  it  was 
the  previous  one.  Several  very  important  consequences 
follow  from  this.  In  the  first  place,  the  larger  area  of 
leaf-surface  evaporates  more  water  than  before,  and  as 
this  water  is  derived  from  the  soil  the  absorbing  surface 
of  the  roots  has  to  increase,  or  the  larger  supplies  need- 
ed could  not  be  obtained.  In  the  second  place,  these 
larger  and  larger  quantities  of  water  require  correspond- 
ing increase  in  the  sectional  area  of  the  pipes  or  water 
conduits — i.  e.,  the  vessels  of  the  wood — through  which 
they  have  to  pass  in  order  to  reach  the  leaves.  This  is 
insured  by  the  increase  in  diameter  of  the  stem  and 
main  root  and  their  chief  branches,  a  larger  number 
of  vessels,  etc.,  being  added  each  season.  In  the  third 
place,  as  the  leaf-crown  enlarges  its  weight  increases, 
and  the  surface  it  exposes  to  the  swaying  action  of  the 
wind  is  correspondingly  greater;  consequently  the  ne- 
cessity arises  for  more  strength  and  rigidity  in  the  sup- 
porting stem,  and  for  a  larger  hold  on  the  soil  on  the 
part  of  the  root-system,  which  has  to  withstand  the 
lever  action  of  the  swaying  tree.  These  needs,  again, 
are  met  by  the  thickening  of  the  woody  parts  of  the 
shoot-axis  and  roots,  and  by  the  greater  spread  and 
increased  number  of  points  of  contact  in  the  soil  of  the 
latter. 

Correlated  with  these  phenomena  we  have  the  in- 
creased leaf-surface  playing  the  part  of  an  enlarging 
manufactory,  which  turns  out  increased  supplies  of  con- 
structive materials  each  summer ;  for  it  is  in  the  leaves 


THE  TREE— ITS  ROOT-SYSTEM.  91 

that  the  substances  for  making  new  roots  and  shoots, 
new  wood,  and  new  leaves,  etc.,  are  constructed.  It  is 
in  the  increased  area  of  this  leaf  laboratory  that  the 
larger  supplies  of  salts,  dissolved  in  the  larger  quantities 
of  water  from  the  soil,  are  brought  into  relations  with 
the  increased  quantities  of  carbonaceous  substance  ob- 
tained from  the  air  in  the  chlorophyll  corpuscles,  and 
consequently  a  larger  yield  of  plant-forming  materials 
is  possible  to  meet  the  demands  of  the  ever-growing 
organs. 

My  present  purpose  is  to  describe  how  the  thicken- 
ing process  occurs  in  the  older  roots,  for  it  is  evident 
at  a  glance  that  the  strong  woody  roots  of  a  large  tree 
have  undergone  many  changes  since  they  were  the  thin 
filiform  rootlets  we  met  with  in  the  young  plant  (see 
Fig.  7).  Not  only  have  they  increased  in  diameter,  but 
they  now  consist  almost  entirely  of  wood,  protected  by  a 
relatively  thin,  brown,  corky  covering,  reminding  one  of 
certain  kinds  of  bark. 

The  first  changes  which  take  place  when  the  young, 
thin  roots  begin  to  thicken  are — first  the  piliferous  layer 
dies  away  and  the  outer  cells  of  the  cortex  turn  brown  ; 
then  a  cylindrical  layer  of  cork  is  developed  in  the  peri- 
cycle,  and  as  this  cork  is  impervious  to  water  it  cuts  off 
the  cortex  from  communication  with  the  axis-cylinder, 
and  consequently  the  cortex  gradually  shrivels  up  and 
is  thrown  off. 

Meanwhile  active  divisions  have  been  going  on  in 
the  cells  immediately  inside  the  phloem  groups  of  the 


92  THE   OAK. 

axis-cylinder  (see  Fig.  5),  and  especially  by  means  of 
tangential  walls.  The  result  of  this  activity  is  the  de- 
velopment of  a  cambium  layer,  as  it  is  called,  immedi- 
ately inside  the  five  phloem  groups  of  the  axis-cylinder, 
and  this  layer  becomes  continuous  all  round  the  axis- 
cylinder,  but  is  so  arranged  that  it  runs  outside  the 
primary  xylem  groups  and  inside  the  primary  phloem 
groups  (Fig.  24,  cam}.  This  cambium  layer  is  a  hollow 
cylindrical  layer  of  thin-walled  cells,  full  of  protoplasm, 
and  somewhat  longer  than  they  are  broad  or  deep,  and 
these  cells  have  the  peculiarity  of  dividing  very  rapidly, 
especially  by  tangential  walls,  so  that  cell  multiplication 
goes  on  very  rapidly,  and  the  layer  would  soon  become 
very  thick  if  no  other  changes  occurred.  As  the  new 
cells  are  formed,  however,  those  on  the  outer  side  of  the 
cylinder — i.  e.,  those  nearest  the  phloem — become  for 
the  most  part  converted  into  sieve-tubes  and  cells  of  the 
phloem ;  while  the  much  more  numerous  cells  formed 
on  the  inner  side — i.  e.,  nearest  the  center  of  the  axis- 
cylinder — are  chiefly  converted  into  vessels  and  cells  of 
the  xylem.  This  xylem  and  phloem  developed  by  the 
cambium  are  termed  secondary  xylem  and  secondary 
phloem  respectively,  and  it  will  be  noticed  that  whereas 
the  secondary  phloem  is  deposited  radially  on  the  inner 
side  of  the  primary  phloem,  the  secondary  xylem  is 
placed  between  the  primary  xylem  groups,  and  not  radi- 
ally outside  them  (Fig.  24,  se.x  and  se.pli).  Moreover, 
the  youngest  vessels  are  now  nearest  the  cambium, 
whence  the  order  of  development  has  become  the  con- 


THE   TREE— ITS   ROOT-SYSTEM.  93 

verse  of  that  of  the  primary  xylem  ;  there  are  also  no 
spiral  vessels  formed  now.  In  fact,  the  structure  of  the 
vascular  bundles  of  the  root  has  now  changed  its  char- 
acter, and  from  this  point  forward  the  root  increases  in 
thickness  exactly  as  the  stem  does,  whence  I  refer  the 
reader  to  the  following  chapter  for  further  details. 

The  development  of  the  layers  of  cork  which  now 
surround  the  thickening  axis-cylinder  go  on  forming 
year  after  year,  as  the  cambium  forms  more  xylem  and 
phloem  and  so  thick  ens  the  root ;  were  this  not  the  case, 
the  layer  of  cork  would  soon  be  ruptured  as  the  root  in- 
creases in  diameter.  Such  rupture,  in  fact,  does  occur, 
but  the  cork-forming  tissue  in  the  pericycle  goes  on 
growing  and  acts  as  a  cork-cambium,  and  repeatedly 
develops  more  cork  to  make  good  the  layers  which  are 
being  split  and  worn  off  in  the  soil. 

From  what  has  been  said  it  will  be  understood  that 
a  transverse  section  of  an  old  root  differs  entirely  in 
structure  from  that  of  a  young  one,  although  all  the 
changes  in  the  former  can  be  correlated  with  the  pri- 
mary structures  of  the  latter.  In  the  first  place,  such  a 
section  shows  no  piliferous  layer  or  cortex,  both  having 
been  sloughed  off  long  ago ;  the  protective  function  of 
these  layers  is  now  assumed  by  the  cork  jacket  (often 
called  periderm)  developed  by  the  cork-cambium  cylin- 
der in  the  pericycle,  and  even  this  will  not  show  all  the 
cork  that  the  cambium  has  developed,  because  many 
outer  layers  will  have  flaked  away,  jiist  as  the  present 
outer  layers  are  doing. 


THE   OAK. 


Then,  inside  this  periderm  we  shall  find  the  phloem 
forming  an  almost  continuous  ring  (Fig.  24,  se.ph),  and 

ep~ 


FIG.  24. — Transverse  sections  (semi-diagrammatic)  of  roots  of  oak,  to  bo 
compared  with  Fig.  7.  The  smaller  figure,  above,  shows  the  cambium 
ring,  com,  now  developed  as  a  continuous  layer  running  inside  the 
primary  phloem,  pr.pli,  and  outside  the  primary  xylem,  pr.x ;  and 
the  larger  figure  shows  the  results  of  its  activity  in  the  formation  of 
secondary  phloem,  se.ph,  inside  the  primary,  and  secondary  xylem, 
ee.x,  between  the  primary  xylem  groups.  In  both  cases,  fp.,  piliferous 
layer;  c,  cortex;  P,  pith  ;  «A,  endodermis.  Within  the  latter  lies  the 
pericycle,  in  which  the  cork  cambium,  c.cam,  is  now  developed. 

consisting  chiefly  of  the  sieve-tubes  and  cells  developed 
from  the  cambium  cylinder,  the  small  primary  phloem 


THE  TREE— ITS  ROOT-SYSTEM.  95 

masses  being  almost  undistinguishably  pressed  into 
(pr.ph). 

In  the  center  of  the  section  will  be  a  small  speck, 
around  which  the  microscopic  primary  xylem  groups 
(pr.x)  are  arranged ;  but  these,  again,  are  merged  be- 
tween the  relatively  huge  masses  of  secondary  xylem 
which  makes  up  by  far  the  major  part  of  the  whole 
(se.x).  The  thin  cambium  ring  can  be  distinguished 
running  between  the  xylem  and  phloem  as  a  fine  line. 
Certain  concentric  annular  lines  may  be  seen  on  the 
section,  and  each  of  these  marks  the  position  in  which 
the  cambium  rested  during  the  winter  of  some  previous 
year.  They  are  the  boundaries  of  concentric  zones, 
termed  annual  rings,  and  the  thickness  of  wood  which 
makes  up  any  one  annual  ring  represents  the  activity  of 
the  cambium  during  that  particular  year. 

Traversing  these  annual  rings  at  right  angles  are  fine 
medullary  rays.  About  five  broader  ones  may  be  found 
corresponding  to  the  radii  on  which  the  primary  xylem 
groups  were  formed,  but  these  are  not  developed  by  the 
cambium  as  the  finer  ones  are.  As  I  shall  have  to  speak 
of  annual  rings  and  secondary  medullary  rays  at  greater 
length  when  describing  the  thickening  processes  in  the 
stem,  and  as  they  are  formed  in  the  same  way  in  both 
cases,  we  may  defer  their  consideration  for  the  present. 

Mention  must  now  be  made  of  a  remarkable  biologi- 
cal phenomenon  in  connection  with  the  roots  of  the  oak. 
This  is  the  very  common  occurrence  of  young  rootlets 
clothed  by  a  fungus  mycelium  ;  the  mycelium  is  found 


96 


THE   OAK. 


as  a  thin  sheet  of  closely-woven  hyphae  continuous  over 
the  whole  of  the  tip,  and  sending  processes  in  between 
the  cells  of  the  dermatogen,  but  not  into  the  cavities  of 
the  cells  nor  deeper  into  the  tissues.  Loose  hyphse  also 


Fio.  25. — Longitudinal  section  of  the  tip  of  one  of  the  roots  marked  ra  in 
Fig.  7,  the  outer  layers  of  which  are  infested  with  fungus  hyph^y 
(mycorhiza);  r.c,  root-cap;  ra,  embryonic  tissue  from  which  all 
originates ;  P,  pith ;  «p,  spiral  vessels  of  the  primary  xylem ;  c, 
cortex. 

radiate  into  the  soil  around,  and  often  simulate  the  root- 
hairs  of  other  plants,  which,  in  fact,  they  are  said  to 
replace  (Fig.  25,/).  These  hyphae  are  extremely  fine 


THE   TREE— ITS  ROOT-SYSTEM.  97 

tubes  of  a  cellulose-like  substance,  filled  with  the  living 
protoplasms  of  the  fungus,  and  possess  the  remarkable 
property  of  being  able  to  bore  their  way  through  or  be- 
tween the  cellulose  walls  of  the  roots.  The  fungus  at- 
tacks the  plant  about  the  second  year,  and  it  is  not  dif- 
ficult to  find  true  root-hairs  on  the  young  root-system 
when  the  apices  are  still  free  from  the  fungus  mycelium. 
The  parts  of  the  root  attacked  alter  their  form  slightly ; 
they  grow  more  slowly  in  length,  and  assume  a  fleshy, 
coral-like  appearance  (Fig.  7,  m).  Such  a  fungus- 
clothed  root  is  called  a  mycorhiza,  and  the  view  is  gain- 
ing ground  that  the  symbiosis  between  the  fungus  and 
the  root  is  of  advantage  to  the  oak.  It  has  even  been 
suggested  that  the  mycelium  performs  the  functions  of 
root-hairs  to  the  root,  absorbing  water  and  nutritive 
materials  from  the  soil  and  passing  them  on  to  the  oak, 
in  return  for  a  certain  small  proportion  of  organic  sub- 
stance which  the  latter  can  well  afford.  At  any  rate,  it 
may  be  that  the  fungus  hurries  the  decomposition  of 
vegetable  remains  in  such  a  way  that  they  become  avail- 
able to  the  root  sooner  than  would  otherwise  be  the  case. 
The  systematic  position  of  these  remarkable  fungi  is  not 
yet  ascertained,  but  there  is  some  evidence  for  the  view 
that  the  mycelium  is  that  of  a  truffle,  though  the  ques- 
tion is  still  an  open  one. 


CHAPTER  VIII. 

THE   TREE — ITS   SHOOT-SYSTEM. 

WHEN  we  cut  into  an  old  branch  or  stem  of  the  oak 
(Fig.  26)  it  is  at  once  obvious  that  considerable  changes 
have  been  produced  since  it  was  a  twig  or  young  shoot- 
axis,  such  as  exists  in  the  young  plant.  Of  these  changes 
the  two  following  are  the  most  conspicuous.  The  pith, 
instead  of  being  surrounded  by  a  cylinder  of  small  vas- 
cular cords,  the  diameter  of  which  hardly  exceeds  its 
own,  as  was  the  case  in  the  one-year-old  shoot-axis  (Fig. 
9),  is  now  a  mere  speck  in  the  middle  of  a  huge  mass  of 
wood  many  hundreds  of  times  as  broad  as  itself,  and  the 
cambium  cylinder  which  was  developed,  as  we  saw,  in 
the  primary  vascular  bundles,  is  now  a  large  (though 
still  thin)  layer  encircling  this  huge  wood  mass.  Again, 
in  place  of  a  delicate  epidermis  surrounding  a  soft,  green, 
cellular  cortex,  as  we  had  in  the  young  stem,  there  is 
here  a  hard,  brown,  rugged  bark,  splitting  off  in  thick 
ridges  on  the  outside. 

The  two  chief  series  of  change  may  be  inferred  from 
comparing  the  two  conditions,  and  taking  into  consider- 
ation all  we  have  learned  so  far.  The  pith  is  the  same 


THE   TREE— ITS   SHOOT-SYSTEM. 


99 


pith  as  before,  and  it  is  the  cambium  cylinder  which 
has  moved  outwards,  as  it  were,  putting  in  all  that 
solid-looking  timber  as  it  did  so.  The  epidermis  and 


FIG.  26. — Photograph  of  the  transverse  section  of  a  log  of  oak,  about  one 
sixth  natural  size.  The  cortex  and  bark  are  removed,  and  the  outline 
is  bounded  by  the  cambium.  The  pith  appears  as  a  mere  dot  in  the 
center;  the  medullary  rays  radiate  from  this,  and  the  annual  rings 
(about  forty  in  number)  are  arranged  concentrically  around  it.  A 
large  crack  has  formed  along  the  plane  of  a  medullary  ray  as  the 
section  dried.  (Muller.) 


the  cortex  of  our  young  stem  have  disappeared,  how- 
ever, their  place  being  taken  by  cork  and  bark.  Closer 
inspection  will  show  that  a  series  of  layers  of  phloem 


100  THE 

has  also  been  formed  between  these  outer  protective 
layers  and  the  cambium. 

We  have  now  to  obtain  some  ideas  as  to  these  curi- 
ous processes  of  increase  in  thickness  of  the  stems  and 
branches. 

The  first  thing  to  insure  this  is  to  understand  the 
constitution  and  behavior  of  the  cambium  cylinder,  for 
it  is  principally  this  tissue  which  brings  about  the 
changes  we  have  to  study. 

We  saw  in  Chapter  IV  that  the  xylem  of  each  pri- 
mary vascular  bundle  is  separated  from  the  phloem  of 
the  same  bundle  by  a  thin  strand  of  cambium  (Figs.  9 
and  12) ;  we  also  saw  that  the  bundles  are  arranged  in  a 
closed  ring  round  the  pith,  and  are  in  their  turn  sur- 
rounded by  the  primary  cortex,  each  being  separated 
laterally  from  its  neighbors  by  a  primary  medullary  ray. 
The  next  point  to  bear  in  mind  is  that  these  medullary 
rays  (like  the  pith  and  cortex)  are  merely  parts  of  the 
general  cell-tissue,  or  fundamental  tissue,  through  which 
the  vascular  bundles  run  upwards  and  downwards  with 
a  tangentially  sinuous  course  from  the  leaves.  The  pri- 
mary medullary  rays,  therefore,  are  merely  spokes,  as  it 
were,  joining  the  pith  and  cortex ;  and  if  we  could  re- 
move the  whole  of  the  vascular  bundles  and  epidermis 
from  the  young  stem  we  should  have  left  a  solid  cylin- 
der of  cell  (pith)  in  the  center,  a  hollow  cylinder  (cortex) 
concentric  to  this,  and  a  space  between  the  two  bridged 
over  at  numerous  places  by  cellular  spokes  (medullary 
rays)  radiating  from  the  pith  to  the  cortex.  Each  spoke 


THE   TREE— ITS   SHOOT-SYSTEM. 


101 


is  very  thin  from  side  to  side,  and  therefore  stands  out 
like  a  knife,  with  an  upper  and  a  lower  edge  (Fig.  27). 
Now  imagine  the  primary  vascular  bundles  replaced. 


FIG.  27. — Tangential  longitudinal  section  of  oak  wood,  magnified  fifty 
diameters,  and  showing  the  transverse  sections  of  the  medullary  rays, 
cut  as  they  project  towards  the  observer.  (Mtlller.) 

The  first  change  is  that  the  cambium  in  the  vascular 
bundles  becomes  continuous  across  through  the  medul- 


102  TUB   OAK. 

lary  rays,  and  so  forms  a  complete  thin  cylinder,  con- 
centric to  the  pith — from  which  it  is  separated  by  the 
breadth  of  the  xylem — and  the  cortex,  from  which  it  is 
separated  by  the  breadth  of  the  phloem. 

The  cells  of  this  cambium  cylinder  go  on  dividing 
continuously  during  the  whole  summer,  until  the 
cylinder  is,  say,  ten  times  as  thick  as  it  was  before. 
Now  suppose  it  to  rest  during  the  winter  and  go  on 
again  next  season,  and  so  on  during  each  successive 
period  of  growth.  Obviously  this  would  realize  one  fact 
in  the  process  we  are  considering — namely,  that  the  stem 
would  grow  in  thickness  year  by  year,  its  diameter  being 
increased  by  twice  the  thickness  of  the  added  cylinder. 

But  to  make  the  above  supposition  accord  with  the 
facts,  we  must  further  picture  to  ourselves  that  when 
the  thickening  cylinder  has  attained  a  certain  thickness, 
a  large  proportion  of  those  of  its  cells  which  lie  on  the 
inside — i.  e.,  nearest  the  pith,  and  therefore  abutting  on, 
lose  their  cambial  nature  and  the  xylem — become  con- 
verted into  elements  of  the  wood ;  while  a  smaller  pro- 
portion of  those  on  the  outer  side  (beneath  the  phloem) 
become  new  phloem  elements.  In  this  way  it  will  be 
seen  that  the  thin  cylinder  of  active  cambium  cell 
travels  outwards ;  ever  receding  radially  farther  from  the 
pith,  and  leaving  xylem  between  itself  and  the  primary 
vascular  bundles  next  the  pith,  and  ever  driving  outwards 
the  primary  phloem  and  cortex,  adding  new  phloem 
elements  (but  in  far  less  proportion)  to  the  inside  of  the 
phloem.  Each  winter  it  pauses  in  this  process,  and 


TUB   TREE— ITS   SHOOT-SYSTEM.  1Q3 

each  spring  it  renews  its  activity.  Further  peculiarities 
will  be  noticed  as  we  proceed. 

Now  let  us  see  what  the  cambium  cells  are,  and  how 
they  change  into  new  elements  of  the  xylem  and  phloem, 
etc.,  respectively. 

Each  cell  of  the  cambium  is  a  thin-walled  prism, 
many  times  longer  than  broad  or  thick,  and  with  its 
ends  brought  to  an  edge  like  that  of  a  thick  chisel,  and 
so  arranged  that  these  edges  run  radially  and  fit  in 
between  those  of  cambium  cells  at  higher  and  lower 
levels.  As  we  have  seen,  the  prism  is  oblong  in  trans- 
verse section.  Each  of  these  cells  contains  protoplasm 
and  a  nucleus,  surrounding  a  sap-cavity,  and  they  are 
nourished  like  other  cells  by  the  substances  brought 
down  from  the  leaves  and  up  from  the  roots,  taking 
what  they  need  from  the  sap. 

"When  a  given  cambium  cell  has  taken  into  its  pro- 
toplasm sufficient  food  materials,  and  has  accomplished 
other  life-processes  under  the  action  of  oxygen,  which  it 
absorbs  dissolved  in  the  water  of  the  sap,  it  grows  larger, 
especially  in  the  radial  direction,  and  then  it  divides 
into  two  cells ;  then  each  of  these  may  repeat  these  pro- 
cesses, and  so  on.  At  last  the  older  ones  can  no  longer 
grow  and  divide,  but  become  changed  into  elements  of 
the  xylem  or  phloem,  according  to  their  position.  All 
the  xylem  thus  produced  by  the  cambium  is  called  sec- 
ondary xylem,  and  the  phloem  secondary  phloem,  and 
so  on,  to  distinguish  them  from  the  primary  structures 
found  in  the  early  stage. 


104  THE   OAK. 

I  now  proceed  to  some  further  details,  which  could 
only  be  rendered  intelligible  in  the  light  of  the  pre- 
ceding preliminary  remarks. 

After  the  cambium  ring  is  once  formed  the  daughter- 
cells  cut  off  on  the  inside  of  the  cambium  always  be- 
come transformed  into  one  or  more  of  the  following 
elements : 

(1)  Some  cambium  cells  which  lie  on  the  radial  con- 
tinuation of  a  medullary  ray  undergo  a  few  horizontal 
divisions  across  the  long  axis,  and  then  simply  pass 
over  as  constituents  of  a  medullary  ray;  as  the  cam- 
bium ring  moves  outward,  in  consequence  of  the  re- 
peated formation  of  thickening  rings,  the  periphery  of 
the  cylinder  of  course  increases,  and  this  allows  of  more 
space  tangentially.  One  consequence  of  this  is  the 
occasional  and  gradual  widening  of  the  medullary  ray 
in  process  of  lengthening ;  this  takes  place  to  a  small 
extent  only.  Another  consequence  of  the  increased 
space  is  the  occasional  interpolation  of  new  medullary 
rays.  Eadial  rows  of  cambial  cells  at  points  which  lie 
between  the  planes  of  two  gradually  diverging  medul- 
lary rays  suddenly  commence  to  form  new  medullary 
rays.  Hence,  as  the  wood  mass  increases  in  radial 
thickness,  more  and  more  of  these  interpolated  medul- 
lary rays  appear,  cutting  up  the  wood  proper  into 
partial  sections.  In  succeeding  years  the  cambium 
keeps  adding  to  the  length  of  these  rays,  as  it  does  to 
that  of  the  older  rays,  and  again  forms  new  ones  be- 
tween as  space  increases.  In  the  same  ring  about  thir- 


THE   TREE— ITS   SHOOT-SYSTEM, 


105 


&\ 


p.v. 


sp. 


FIG.  28. — The  various  chief  elements  of  the  wood  of  the  oak,  isolated  by 
maceration,  and  highly  magnified :  y,  a  fiber,  distinguished  by  its 
thick  walls,  simple  slit-like  pits,  and  no  contents ;  w.p,  part  of  a  row 
of  wood-parenchyma  cells,  with  simple  pits,  and  containing  starch  in 
winter ;  tr,  a  tracheid,  distinguished  from  the  fiber  especially  by  its 
bordered  pits ;  p.v,  part  of  a  rather  large  pitted  vessel,  made  up  of 
communicating  segments,  each  of  which  corresponds  to  a  tracheid, 
and  has  bordered  pits  on  its  walls ;  sp,  part  of  a  spiral  vessel. 


106  TUB   OAK. 

teen  rays  to  the  millimetre  may  be  counted  on  the  trans- 
verse section  of  the  wood. 

(2)  The  cambium  cells  situated  between  the  rays — 
except  when  they  suddenly  commence  to  form  a  new 
ray,  as  just  described — pass  over  into  one  or  more  of 
the  following  elements  of  the  wood  proper — viz.,  wood- 
parenchyma,  libriform  fibers,  tracheids,  segments  of  the 
vessels  (see  Fig.  28). 

When  a  cambium  cell  passes  over  into  wood-paren- 
chyma it  first  undergoes  a  few  horizontal  divisions  trans- 
verse to  its  long  axis,  and  then  we  have  a  vertical  row  of 
five  or  six  parenchymatous  cells,  the  walls  of  which  do 
not  thicken  much,  but  obtain  small  simple  pits,  and  re- 
tain part  of  their  living  contents — protoplasm,  nucleus, 
starch-forming  corpuscles,  etc. — and  indeed  present 
much  resemblance  to  the  cells  of  the  medullary  rays 
themselves. 

When  the  cambial  cell  becomes  transformed  into  a 
libriform  fiber  it  does  this  simply  by  thickening  its  walls 
at  the  expense  of  the  living  contents,  etc.,  which  soon 
disappear.  The  cell  undergoes  no  horizontal  divisions, 
and  probably  elongates  very  slightly.  The  thickened 
walls  become  pitted  with  minute  simple  pits,  and  are 
stratified  and  eventually  lignified. 

In  the  case  of  the  transformation  of  a  cambial  cell 
into  a  tracheid  everything  is  essentially  as  described  in 
the  last  paragraph,  except  that  the  diameter  increases 
and  the  thickening  walls  become  marked  with  bordered 
pits,  quite  similar  to  those  of  the  pine,  except  that  they 


THE  TREE— ITS  SHOOT-SYSTEM.  107 

are  more  numerous,  are  not  confined  to  the  radial  walls, 
and  they  are  not  quite  circular,  but  have  an  oval  shape 
with  a  slit-like  aperture  to  the  border,  the  long  axis  of 
the  slit  being  nearly  transverse  to  the  long  axis  of  the 
tracheid. 

In  the  conversion  of  cambium  cells  into  vessels  the 
chief  point  to  note  is  that  the  vessel  is  essentially  a  ver- 
tical row  of  superposed  tracheids — each  of  which  has 
been  developed  from  a  cambium  cell  as  just  described — 
the  oblique  separating  walls  of  which  become  almost  en- 
tirely obliterated.  The  markings,  thickening,  and  want 
of  contents  are  as  in  the  case  of  tracheids,  the  chief  dif- 
ference being  the  more  pronounced  growth  in  diameter 
of  the  vessel  segments,  especially  those  formed  in  the 
spring  wood. 

It  will  readily  be  understood  that  the  growth  in  diam- 
eter of  these  vessel  elements  exerts  a  disturbing  effect 
on  the  radial  arrangement  of  the  other  elements  of  the 
wood,  and  the  displacements  and  compression  of  the 
latter  are  considerable  and  various,  so  that,  at  length, 
very  little  trace  of  the  original  order  is  observable.  It 
not  unfrequently  happens,  however,  that  many  suc- 
cessive rows  of  the  fibers  or  tracheids  are  formed  in  the 
outer  parts  of  the  annual  ring,  and  in  such  cases  the 
original  radial  series  can  be  detected. 

There  are  several  other  points  also  to  be  noted  in  the 
development  of  secondary  wood.  In  the  first  place,  the 
various  elements  do  not  maintain  an  exact  vertical  posi- 
tion, but  may  lean  over  both  in  the  radial  and  in  the 


108  THE   OAK. 

tangential  directions.  These  slight  displacements  from 
the  vertical  are  chiefly  due  to  the  fact  that  the  elements 
— fibers,  tracheids,  and  vertical  groups  of  wood-paren- 
chyma— have  not  finished  their  growth  in  length  when 
they  pass  over  from  the  cambial  condition  ;  consequently 
the  pointed  ends  of  the  elongating  fibers,  etc.,  push 
themselves  between  the  ends  of  others  which  lie  above 
and  below  them,  and  a  slight  tilting  from  the  vertical 
results.  This  may  be  sufficient  to  produce  a  twisting  of 
the  stems  and  branches  which  is  visible  even  to  the  un- 
aided eye. 

Another  important  point  is  that  the  length  of  the 
elements,  as  well  as  their  diameters,  vary  at  different 
periods  in  the  life  of  the  tree. 

First  as  to  the  diameter.  The  fibers  and  tracheids 
developed  in  the  autumn  have  a  relatively  smaller  radial 
diameter  than  those  formed  earlier,  and  this,  combined 
with  the  fact  that  those  elements  which  develop  in  the 
spring  have  the  relatively  largest  diameters,  alone  would 
suffice  to  mark  the  boundary  between  any  two  annual 
rings.  But  the  same  holds  good  for  the  vessels ;  those 
formed  in  the  spring  wood  are  very  large  compared  with 
those  formed  later — the  latter  are  also  more  sparely  de- 
veloped— whence  the  contrast  at  the  boundary  between 
the  annual  rings  is  intensified.  With  the  diminution  in 
relative  diameter  of  the  tracheids  and  fibers  a  correspond- 
ing increase  in  the  thickness  of  their  walls  is  connected 
— a  phenomenon  which  again  intensifies  the  contrast 
between  adjacent  annual  rings. 


THE  TREE— ITS  SHOOT-SYSTEM.  109 

But,  in  addition  to  these  differences  in  diameter  with- 
in one  and  the  same  annual  ring,  a  gradual  increment 
in  the  average  size  of  certain  of  the  elements  (both  in 
length  and  diameter)  occurs  as  the  tree  becomes  older — 
in  other  words,  the  average  width  and  length  of  the  ele- 
ments increases  year  by  year  up  to  a  certain  age  ;  after 
reaching  a  definite  size  they  enlarge  no  more.  These 
changes  differ  according  to  the  part  of  the  tree  con- 
cerned. In  the  stem  of  the  oak  the  chief  changes  in 
this  connection  are : 

The  fibers  increase  in  length  as  follows,  according  to 
Sanio's  measurements :  While  they  average  0-43  mm.  in 
length  in  the  first  annual  ring,  they  increase  to  0-60 
mm.  in  the  second,  0*74  mm.  in  the  fourth,  and  go  up 
to  1-22  mm.  after  a  great  age  (one  hundred  and  thirty 
years  ?)  The  tracheids  in  the  same  annual  rings  were 
found  to  average  0-39,  0-43,  O53,  and  0'72  mm.  respect- 
ively ;  and  the  individual  members  or  segments  of  the 
argar  vessals  averaged  0-25  mm.  in  the  second  annual 
ring,  0-26  mm.  in  the  fourth,  and  0*36  mm.  in  the  three 
outer  rings.  The  mean  radial  diameter  of  these  vessels 
also  increased :  in  the  third  year  it  was  0-08  mm.,  and  it 
rose  year  by  year  until  in  the  sixth  year  the  definitive 
width  of  0-31  to  0-33  mm.  was  attained.  After  this  the 
width  of  these  vessels  is  practically  constant.  These  in- 
crements in  size  appear  to  take  place  after  the  element 
has  passed  out  of  the  strictly  cambial  condition. 

The  passage  of  the  older  wood  in  the  center  of  the 
stem  into  the  condition  known  as  "  heart- wood  "  (dura- 


HO  TEE   OAK. 

men)  as  opposed  to  "  sap-wood  "  (alburnum)  is  not  at- 
tended with  any  profound  anatomical  changes ;  the  chief 
alterations  are  of  the  nature  of  infiltration  by  foreign 
chemical  substances,  and  alteration  in  the  physical  prop- 
erties of  the  cell-walls  and  in  the  contents.  These 
changes  are  somewhat  sudden,  and  the  fact  that  starch 
ceases  to  be  deposited  in  this  altered  wood  helps  to  in- 
dicate that  the  change  is  one  of  degradation — the  cells 
of  the  softer  tissues  have  ceased  to  be  "  alive,"  and  the 
"  heart "  commences  to  undergo  degradation.  At  the 
same  time,  although  we  must  regard  the  "  heart "  as 
dead,  it  is  very  resistant,  perhaps  owing  to  the  preserv- 
ative action  of  infiltrated  bodies. 

A  remarkable  phenomenon  which  may  be  noticed 
here  is  the  filling  up  of  the  older  large  vessels  with 
tyloses.  These  are  thin-walled,  bladder-like  vesicles 
projecting  into  the  cavity  of  the  vessel  from  the  bor- 
dered pits,  and  are,  in  fact,  due  to  the  protrusion  into 
the  cavity  of  the  thin- walled  parenchyma  cells,  which 
drive  the  pit  membrane  in  and  then  swell  up.  At  the 
planes  of  contact  between  various  tyloses  from  opposite 
points  on  the  wall  of  the  vessel  the  tyloses  are  flattened, 
and  the  appearance  is  very  like  that  of  a  parenchyma- 
tous  tissue  (Fig.  29,  d).  When  young  the  tyloses  are 
found  to  contain  a  nucleus,  protoplasm,  and  cell-sap,  and 
they  are  known  to  form  division  membranes  and  divide 
like  cells  of  the  pith  or  cortex  ;  later  on  they  lose  their 
contents  and  form  a  sort  of  packing  in  the  by  this  time 
functionless  vessel. 


THE   TREE— ITS  SUOOT-SYSTEJI. 


Ill 


During  the  whole  time  of  the  activity  of  the  cam- 
bium ring  and  the  formation  of  wood  on  its  interior,  it 
must  not  be  forgotten  that  the  outer  rows  of  cambial 
cells  are  passing  over  into  the  tissue  known  as  bast  or 
secondary  phloem  (also  called  secondary  cortex);  the 
chief  differences  in  the  process  being  (1)  that  much 


FIG.  29. — A  small  piece  of  one  annual  ring  of  old  oak  wood  (magnified 
twenty  diameters) :  a,  boundary  of  the  autumn  wood  of  the  preced- 
ing (older)  ring;  b,  that  between  the  zone  shown  and  the  next 
youngest  ring.  In  the  annual  ring  shown  the  spring  wood  begins 
with  large  vessels,  c  and  d,  some  with  tyloses,  <?,  in  them,  and  passes 
gradually  into  autumn  wood,  with  smaller  vessels,  <?,  e,  and  more 
tracheids  and  fibers,  g.  Only  small  medullary  rays,  «',  are  shown. 
(Hartig.) 

less  phloem  than  xylem  is  formed ;  (2)  that  the  ele- 
ments do  not  become  lignified ;  and  (3)  that  the  dis- 
turbances in  the  arrangement  of  the  elements  are  more 
profound  from  the  continued  pressure  exerted  upon 
them  between  the  resistant  wood  and  the  elastic  peri- 
derm  and  bark,  on  the  one  hand,  and  the  increased  ex- 
tension tangentially  which  it  undergoes  as  the  thicken- 


112  THE   OAK. 

ing  mass  of  wood  drives  it  outwards,  on  the  other.  The 
other  differences  chiefly  concern  the  individual  elements 
now  to  be  described. 

All  that  was  said  of  the  medullary  rays  in  the  wood 
applies  also  to  those  in  the  bast ;  the  cambium  in  keep- 
ing open  or  originating  new  medullary  rays  does  so  on 
both  sides,  and  therefore  the  medullary  rays  are  to  be 
traced  radially  through  the  cambium  from  wood  to  cor- 
tex. The  rays  in  the  bast  are  termed  "  bast  rays  "  ;  the 
broader  ones  contain  isolated  groups  of  sclerotic  cells 
and  cells  containing  crystals. 

The  changes  which  the  radial  rows  of  cells  on  the 
exterior  of  the  cambium  zone  undergo  to  form  the  ele- 
ments of  the  secondary  phloem  are  as  follows  : 

(1)  Bast  parenchyma  (Fig.  17,  b  p)  is  developed,  like 
the  wood  parenchyma,  from  cambium  cells  which  un- 
dergo a  few  transverse  divisions  and  then  pass  over  as 
longitudinal  groups  of  cells,  which  retain  their  living 
contents,  etc.     From  these  longitudinal  groups,  accom- 
panying the  sieve-tubes  as  parallel  series,  they  are  called 
companion  cells  (cambiform  cells). 

(2)  Sieve-tubes  (Fig.  18,  bp],  which  may  be  regarded 
as  homologous  with  the  vessels  of  the  wood,  and,  like 
those,  are  constituted  of  series  of  segments.     Each  seg- 
ment corresponds  to  a  cambium  cell,  and  is  obliquely 
tapering  at  the  end  where  it  fits  on  to  another  segment. 
These  dividing  septa  are  not  completely  broken  through, 
as  in  the  case  of  the  wood-vessels,  however,  but  are 
pierced  by  a  grating-like  series  of  holes   (the  sieve) 


TH3   TREE— ITS   SHOOT-SYSTEM.  H3 

through  which  the  protoplasmic  and  other  contents  of 
the  continuous  segments  pass  uninterruptedly.  Similar 
sieve-plates  occur  on  the  lateral  walls  of  the  segments 
also.  The  walls  are  not  thickened  and  not  lignified,  and 
thus  the  morphological  similarities  between  the  sieve- 
tubes  of  the  bast  and  the  vessels  of  the  wood  (which  only 
contain  air  and  water,  have  their  septa  absorbed,  and 
their  walls  lignified  and  covered  with  bordered  and  sim- 
ple pits)  depend  almost  entirely  on  the  similar  develop- 
ment. The  sieve-pores  are  very  fine,  and  easily  over- 
looked. 

(3)  The  bast  fibers  (Figs.  17  and  18  £),  which  are 
homologous  with  the  libriform  fibers  of  the  wood,  and 
are  developed  in  the  same  way  from  single  cells  of  the 
cambium.  They  are  short,  blunt,  very  thick-walled 
fibers,  grouped  in  strands  which  appear  on  the  trans- 
verse section  of  the  bast  as  tangential  bands  2-4  deep, 
alternating  (in  the  radial  direction)  with  broader  bands 
of  sieve-tubes  and  parenchyma.  These  bands  of  fibers 
(hard  bast)  are  accompanied  at  their  outer  and  inner 
boundaries  by  parenchyma-like  cells  arranged  in  vertical 
rows,  each  of  which  contains  a  large  simple  crystal  of 
calcium  oxalate  imbedded  in  yellowish  substance,  and 
the  walls  of  which  are  slightly  sclerotic.  Similar  verti- 
cal series  of  cells  are  found  in  the  soft  bast,  but  they  con- 
tain compound  (clustered)  crystals  of  the  same  salt  (Figs. 
17  and  18,  e). 

The  soft  bast  also  contains  scattered  roundish  groups 
of  short  sclerenchyma  cells,  the  thickened  walls  of  which 


114  TUE   OAK. 

are  traversed  by  very  numerous  pit-canals ;  cells  contain- 
ing crystals  also  accompany  these  groups. 

In  consequence  of  the  above  arrangements  the  second- 
ary cortex  presents  a  more  or  less  stratified  appearance 
on  the  transverse  section,  the  strata  consisting  chiefly  of 
alternate  tangential  layers  of  hard  bast  and  soft  bast 
(Fig.  17) ;  the  elements  of  the  latter  also  showing  a  de- 
cided tendency  to  be  arranged  in  layers. 

After  the  first  year  the  young  stem  or  branches  cov- 
ered with  thin  periderm  are  seen  to  be  dotted  with  len- 
ticels  or  cortical  pores.  Structures  similar  in  every  re- 
spect and  subserving  the  same  function — viz.,  the  ex- 
change of  gases  with  the  environment — are  formed  on 
the  roots  as  soon  as  the  periderm  is  developed. 

The  lenticel  is  a  local  interruption  of  the  periderm, 
where  the  cells  are  loosened  so  as  to  allow  air  to  pass 
between  the  loosened  cells  into  the  intercellular  spaces 
between  the  cortical  cells.  Each  lenticel  may  be  de- 
scribed as  a  biconvex  projecting  swelling  of  the  peri- 
derm, the  swelling  being  caused  by  the  increased  radial 
diameter  of  the  loosened  cells.  '  This  is  the  condition 
during  the  spring  and  summer,  but  in  the  winter  the 
cork -cambium  is  continuous  across  beneath  the  leuticel, 
and  forms  periderm  in  an  uninterrupted  sheet,  to  be 
ruptured  again  at  the  lenticel  during  the  formation  and 
swelling  of  the  looser  cells  (complementary  or  packing 
cells)  in  the  following  spring.  These  loose  packing-cells 
are  at  first  quite  similar  to  young  cork-cells,  and  are  de- 
veloped as  such,  but  they  loosen  and  round  off,  and  their 


TIIE   TREE— ITS   SHOOT-SYSTEM.  H5 

cell-walls  do  not  become  completely  suberized  for  a  long 
time,  but  are  capable  of  swelling ;  in  fact,  the  rounding 
off  depends  on  the  absorption  of  water  by  the  cellulose 
walls  and  contents.  The  outer  parts  of  the  older  len- 
ticel  openings  are  thrown  off  with  the  bark-scales,  but 
the  inner  parts  remain,  and  can  be  found  between  the 
scales  in  older  branches,  in  the  fissures. 

The  first  points  of  origin  of  lenticels  are  usually 
beneath  the  stomata,  and  the  lenticels  may  be  regarded 
as  devices  for  prolonging  the  passages  of  the  stomata 
through  the  thickening  periderm  year  by  year.  The 
cortical  cells  beneath  the  stoma  become  rneristematic — 
in  effect  they  continue  the  phellogen  below  the  stoma, 
only  they  divide  less  regularly  and  in  all  directions.  The 
daughter-cells  thrown  off  externally  swell  up  and  pro- 
trude, driving  the  stomatic  cells  outwards  and  apart,  and 
emerging  between  the  ruptured  guard-cells  as  the  first 
packing-tissue.  The  phellogen  or  cambium  of  the 
lenticel  forms  phelloderm  on  its  interior  in  continuation 
of  that  formed  by  the  rest  of  the  cork-cambium.  The 
protruding  packing-cells  dry  up  eventually,  and  form 
the  powdery  substance  seen  between  the  gaping  lips  of 
older  lenticels.  In  the  autumn  the  cells  formed  by  the 
meristem  below  the  packing-cells  do  not  separate,  but 
are  suberized  and  closely  and  radially  arranged  like  the 
rest  of  the  cork :  in  fact,  they  continue  the  cork  layer 
as  a  closing  layer  beneath  the  lenticel,  thus  protecting 
the  tissues  beneath  through  the  winter.  In  the  follow- 
ing spring  new  layers  of  loose,  swelling  packing-cells 


116  THE   OAK. 

are  developed  again,  and  these  absorb  water  and  bulge, 
bursting  the  closing  layer  and  reopening  the  lenticel 
for  the  season.  As  the  branch  ages  and  its  surface  in- 
creases new  lenticels  are  developed  between  the  earlier 
ones,  and,  of  course,  with  no  reference  to  stomata. 

The  exterior  of  the  very  young  stem  or  branch  is 
smooth  or  slightly  pubescent,  the  green  color  gradually 
passing  into  a  silver-gray  as  the  periderm  develops,  and 
in  a  few  years  (when  the  shoot  is  from  five  to  twenty 
years  old,  or  thereabout)  the  gradually  thickening  bark 
is  shining  and  turning  browner,  necked  with  leuticels 
and  lichens.  Later  still  the  bark  is  rugged,  brown,  and 
fissured,  and  usually  covered  with  small  lichens  and 
fungi.  Bark  begins  to  exfoliate  at  about  the  thirtieth 
year. 

The  epidermis  cracks  and  peels  off  when  the  twigs 
are  a  year  old,  and  shreds  of  the  dead  membrane  may 
be  detected  on  the  outside  of  the  young  cork,  which 
begins  to  form  very  early  during  the  first  year.  It  is, 
in  fact,  owing  to  the  impervious  nature  of  this  cork  that 
the  epidermis  dies,  and  to  the  stretching  of  the  cortex 
as  the  stem  grows  in  thickness  that  the  dead  membrane 
cracks  and  peels  off  (see  Figs.  17  and  18). 

The  first  indication  of  the  development  of  the  cork 
is  the  conversion  of  the  sub-epidermal  layer  of  cortex- 
cells  into  a  meristem — i.  e.,  the  cells  become  capable  of 
active  growth  and  division. 

Each  cell  of  the  layer  referred  to  may  be  termed  an 
initial  cell  of  the  cork-cambium  (or  phellogen),  and  the 


THE   TREE— ITS   SHOOT-SYSTEM.  Hf 

layer  may  be  called  the  initial  layer.  This  layer  behaves 
essentially  like  the  cambium  of  a  fibro- vascular  bundle, 
except  that  its  daughter-cells  become  cork  and  phel- 
loderm  instead  of  phloem  and  xylem. 

The  first  event  to  notice  is  that  each  of  the  initial 
cells  grows  radially,  and  divides  by  a  tangential  wall 
into  an  inner  cell  nearest  the  axis  of  the  branch  and  an 
outer  cell  nearer  the  epidermis ;  the  outer  cell  becomes 
forthwith  a  cork-cell — i.  e.,  its  contents  die  and  mostly 
disappear,  and  the  cellulose  cell-wall  becomes  suberized 
— the  inner  cell  remains  capable  of  repeating  the  pro- 
cess. But  this  is  not  the  only  case.  After  the  division, 
as  before,  of  the  initial  cell,  it  may  happen  that  the  inner 
cell  becomes  transformed  into  a  collenchymatous  cortical 
cell  containing  chlorophyll,  and  it  is  the  outer  of  the 
daughter- cells  which  retains  the  meristem  character 
and  acts  again  as  a  phellogen  cell,  cutting  off  daughter- 
cells  sometimes  on  one  side  and  at  others  on  the  other. 
Thus,  in  the  oak,  the  phellogen  gives  rise  to  permanent 
tissue  on  both  side,  of  the  initial  layer :  those  cells  which 
lie  on  the  inside  become  phelloderm  (cortical  cells),  those 
on  the  outside  become  transformed  into  phellem  (cork). 
The  three  tissues,  phelloderm,  phellogen,  and  phellem, 
are  called  the  periderm. 

It  is  obvious  that  the  cork-cambium,  by  thus  adding 
to  the  cortical  parenchyma,  is  gradually  driven  radially 
outwards  from  the  center  of  the  stem.  This  means  that 
it  obtains  room  to  extend  tangentially,  and  it  does  this 
by  its  cells  occasionally  dividing  by  walls  perpendicular 


118  THE   OAK. 

to  the  far  more  numerous  tangential  walls.  It  is  also 
easy  to  see  that  the  cork-cells  must  be  arranged  in 
radial  rows,  and  this  arrangement  is  very  conspicuous 
(Fig.  18).  The  earlier  cork-cells  have  very  thin  walls, 
later  ones  have  the  walls  thicker. 

After  the  development  of  the  first  layer  of  cork  the 
stretched  epidermis  dies,  and  forms  simply  a  dead  mem- 
brane outside  the  thin  cork.  In  succeeding  years 
layers  of  phellogen  are  formed  annually  beneath  the 
older  ones,  and  thus  the  cork  layers  increase.  Moreover, 
since  the  successive  layers  cut  out  thin,  scale-like  areas 
of  cortex,  trapping  them,  as  it  were,  between  the  present 
and  the  preceding  cork,  the  thickening  corky  covering 
is  stratified — consists  of  successive  and  obliquely  over- 
lying thin  sheets  of  dead  cortex  and  cork  proper  (Fig. 
30).  Again,  since  the  increase  in  thickness  of  the  stem 
or  branch  is  continually  driving  these  corky  and  .dead 
structures  outwards,  they  at  length  crack,  and  form  the 
fissured  bark  found  on  older  parts.  Bark  is  thus  seen 
to  be  something  more  than  cork,  or  even  periderm,  and 
it  is  defined  to  be  all  the  dead  tissues  cut  out  by  the 
phellogen. 

It  is  also  to  be  noticed  that  the  successive  phellogen 
layers  of  different  years  are  not  concentric,  but  the  new 
ones  cut  the  old  ones  at  acute  angles  (Fig.  30),  thus  cut- 
ting out  scale-like  areas  of  cortex ;  the  consequence  of 
this  is  the  formation  of  the  very  irregular  scales  of  bark 
thrown  off  from  the  older  stems  and  branches  of  the 
oak.  It  follows  from  what  has  been  said  that  in  older 


THE   TREE— ITS  SHOOT-SYSTEM. 


119 


120  THE   OAK. 

trees  the  pliellogen  layers  may  be  formed  so  far  down  in 
the  cortex  that  they  cut  out  tissues  of  the  secondary  cor- 
tex— i.  e.,  phloem  and  bast  fibers.  It  is,  of  course,  this 
gradual  exfoliation  of  the  cut-out  areas  of  bark  that  ex- 
plains the  relative  thinness  of  the  bark  in  very  old  stems 
and  branches ;  the  whole  of  the  primary  cortex,  and  most 
of  that  formed  from  the  cambium,  have  been  thrown 
off  as  bark  long  before. 


CHAPTER  IX. 

THE  TREE   (continued],    INFLORESCENCE  AND   FLOW- 
ERS—FRUIT AND  SEED. 

THE  oak  flowers  in  May  in  this  country,  the  young 
inflorescences  developing  as  the  leaves  unfold.  The 
flowers  are  unisexual,  both  male  and  female  appearing 
on  the  same  branches — i.  e.,  the  tree  is  monoecious — and 
even  on  the  same  twigs  of  the  current  year.  The  rule 
is  that  the  apical  bud  of  a  last  year's  twig  produces 
a  few  male  inflorescences  from  between  the  axils  of  the 
upper  scales,  and  then  grows  out  into  a  green  twig 
bearing  about  six  to  ten  normal  leaves,  the  female  inflo- 
rescences arising  from  the  axils  of  two  or  three  of  the 
upper  leaves  (Figs.  31  and  32).  Lateral  buds  below  the 
terminal  bud  of  the  last  year's  twig  usually  produce  male 
inflorescences  only — a  phenomenon  in  accordance  with 
their  feeble  development  generally.  Thus  the  male  in- 
florescences are  produced  first — a  common  occurrence  in 
forest  trees. 

Since  the  inflorescences  arise  from  the  axils  of  leaves, 
their  arrangement  accords  with  the  phyllotaxis  of  the 
tree — i.  e.,  | — so  far  as  it  goes.  It  should  be  borne  in 
mind  that  the  bud-scales  are  stipules. 


122 


THE   OAK. 


The  male  inflorescences  hang  down  from  between 
the  bud-scales  as  simple  catkin-like  spikes,  each  bear- 
ing about  a  dozen  flowers.  Each  male  flower  springs 


FIG.  31.— A  sprig  of  oak  in  May,  with  the  pendent  male  catkin  below, 
and  the  minute  spikes  of  female  flowers  just  showing  above.  (Th. 
Hartig.) 

from  the  axil  of  a  tiny  scale-like  bract,  and  consists  of 
a  shallow  perianth,  unequally  divided  into  about  five  to 
seven  small  linear-lanceolate  lobes,  inclosing  about  five 
to  twelve  stamens ;  there  is  no  trace  of  an  ovary.  The 
number  of  lobes  of  the  perianth  varies,  as  also  does  the 
number  of  stamens ;  the  former  are  covered  with  short 
hairs. 


INFLORESCENCE  AND  FLOWERS— FRUIT  AND  SEED.    123 

Each  of  the  stamens  consists  of  a  slender  thread 
(filament)  bearing  on  its  top  a  four-chambered  swollen 
anther.  This  contains  a  yellow  dust,  the  pollen,  com- 
posed of  round  grains  (pollen  grains),  each  with  three 
thinner  spots  in  its  otherwise  thick  wall.  Each  of  these 
pollen  grains  consists  of  a  membrane  inclosing  nucleated 
protoplasm  and  food  materials.  When  ripe  the  wind 
blows  the  pollen  as  it  scatters  from  the  dangling  stamens, 
and  some  of  the  grains  reach  the  stigmas  of  the  female 
flowers ;  here  they  germinate,  each  pollen  grain  sending 
a  delicate  pollen-tube  down  the  style  into  the  ovary  of 
the  flower.  This  process  of  application  of  the  pollen 
grains  to  the  stigma  is  termed  pollination,  and  depends 
on  the  wind. 

The  female  inflorescences  are  also  spikes  (Fig.  32,  A), 
but  they  bear  only  one  to  five  flowers,  and  stand  off 
from  the  axils  of  the  foliage  leaves.  In  the  commonest 
English  variety  ( Q.  pedunculata)  the  spikes  are  rather 
long,  obliquely  erect,  and  the  flowers  are  scattered  on 
the  upper  end  of  the  rachis  of  the  spike ;  in  other  varie- 
ties the  flowers  are  more  clustered  in  the  axils  of  the 
leaves.  Here,  as  in  one  or  two  other  details,  minute 
differences  are  apparent  in  different  individuals ;  similar 
trifling  differences  are  met  with  in  the  structure  of  the 
male  flowers. 

Each  female  flower  springs  (like  the  male)  from  the 
axil  of  a  small  bract :  in  other  respects  it  is  very  unlike 
the  male  flower.  In  the  first  place,  the  ovary  is  inferior, 
being  sunk  in  and  fused  into  a  six-partite  perigone,  the 


124 


THE   OAK. 


teeth  of  which  project  some  distance  up  and  surround  a 
trifid  stigma  (Figs.  33  and  34,  6-).  One  of  the  lobes  of 
the  perigone  will  be  found  opposite  to  the  bract ;  the 
three  lobes  of  the  stigma  are  superposed  on  three  alter- 
nate (outer)  lobes  of  the  perigone. 


FIG.  32.— A,  Flowering  twig  and  inflorescences,  male  ( t ),  and  female  ( 5 ), 
semi-diagrammatic.  B,  Diagram  of  plan  of  a  similar  but  lateral  twig. 
F.  Leaf  from  axil  of  which  the  twig  arises :  x,  parent  stem ;  a  and  /3, 
bracts.  The  numbers  1-11  denote  pairs  of  stipules  acting  as  bud- 
scales,  some  with  male  inflorescences  (j)  springing  from  between 
them;  the  continued  numbers  12-21  also  denote  pairs  of  stipules,  but 
these  have  their  accompanying  leaves,  with  or  without  female  inflo- 
rescences ( 9  )  in  the  axils.  (Eichler.) 


There  is  yet  a  further  covering  to  the  female  flower. 
The  somewhat  irregular  margins  of  a  minute  cup-like 
investment  are  to  be  seen  arising  from  beneath  and 
around  the  perigone :  this  is  the  scaly  cupula,  the  future 
"cup"  in  which  the  "acorn"  is  inserted  (Fig.  34,  m). 
If  the  young  female  flower  is  carefully  bisected  longi- 


INFLORESCENCE  AND  FLOWERS— FRUIT  AND  SEED.    125 

tudinally  this  cupule  will  be  seen  to  consist  of  a  ring  of 
tissue,  arising  from  beneath  the  ovary,  and  with  its 
margin  notched  into  scales.  As  the  ovule  enlarges 
the  minute  scales  become  more  numerous,  new  ones 
arising  at  the  inner  margin  of  the  up-growing  cupule. 

A  transverse  section 
across  the  female  flower 
at  a  slightly  later  period 
shows  that  the  inferior 
ovary  is  divided  into 
three  chambers  (loctili), 
each  corresponding  to 
one  of  the  lobes  of  the 
stigma,  and  each  con- 
taining two  ovules  (Fig. 

34).    These  Ovules  are  in-    FlG\33r:A  g™up -of  female  flowers 

(slightly  magnified).    Each  has  a 

Serted  at  the  upper  part         spreading  stigma  above  and    the 

of  the  inner  angle  of  the       co«ins   cuPu}e  below'.  an<J 

arises  from  the  axil  ot  a  pointed 

chamber,  and  thus  hang       bract.   (Th.  Hartig.) 
down  in  pairs.   A  curious 

point  arises  here.  It  seems  that  at  the  period  when  the 
female  flower  has  just  opened,  but  has  not  yet  received 
any  pollen  on  its  stigma,  neither  the  ovules  nor  the 
chambers  are  as  yet  formed,  and  the  segments  of  the 
perigone  spring  from  the  lower  portion  of  the  flower, 
and  this  condition  is  not  altered  until  pollination  oc- 
curs ;  then  the  tissue  below  the  stigma  becomes  the 
three-chambered  ovary  sunk  in  the  perigone. 

The  pollination  takes  place  in  May-June,  and  ferti- 


126 


THE   OAK. 


lization  soon  afterwards ;  in  July  the  young  acorns  can 
be  made  out  peeping  from  the  cupules  in  which  they  had 
hitherto  been  inclosed.  The  acorn  reaches  its  full  size 
towards  the  end  of  September,  and  ripens  and  falls  in 


FIG.  34.— Female  flower  in  section.  To  the  left  three  transverse  sections 
through  the  young  ovary;  the  lower  one  showing  the  three  placentas, 
each  with  two  ovules.  To  the  right,  three  longitudinal  median  sec- 
tions through  the  whole  flower  at  successive  periods:  a,  stigma-,  ft, 
carpal ;  c,  perianth ;  d,  cavity  of  ovary  with  ovules ;  m,  the  cupule. 
(Th.  Hartig.) 

October.  When  ripe  the  acorn  is,  as  we  have  seen,  an 
ovoid,  smooth,  olive-brown  nut,  with  the  broad  end  in- 
serted into  the  cupule,  and  the  narrower,  somewhat 
tapering  end  projecting  free. 


INFLORESCENCE  AND  FLOWERS— FRUIT  AND  SEED.    127 

It  will  be  interesting,  in  the  light  of  the  foregoing 
remarks,  to  examine  one  of  the  stronger  lateral  buds  of 
the  oak  towards  the  end  of  April,  before  it  unfolds.  A 
transverse  section  of  such  a  bud  shows  the  following 
structures  :  In  the  centei  is  the  axis  of  the  young  shoot, 
represented  by  the  small  central  dot  in  the  diagram 
(Fig.  32,  B).  Surrounding  this  are  about  eight  to  ten 
green  leaves  in  section,  and  folded  on  their  midribs  in 
such  a  way  that  the  two  halves  of  the  upper  surface  are 
face  to  face  and  somewhat  crumpled  ;  some  of  these  are 
turned  so  that  their  edges  are  directed  one  way,  others 
with  them  directed  the  other. 

Each  of  these  leaves  has  a  pair  of  small  stipules,  also 
cut  across,  and  rather  difficult  to  identify  (Fig  32, 12-20). 
Some  of  the  foliage  leaves  bear  female  inflorescences  in 
their  axils,  as  indicated  by  the  sign  $  in  the  figure.  Fol- 
lowing on  these  stipulate  leaves  are  a  number  of  pairs  of 
larger  stipules,  devoid  of  foliage  leaves  and  constituting 
the  bud-scales  (Fig.  32,  1-11).  Some  of  these  bear  male 
inflorescences  (  $  )  between  them — i.  e.,  in  the  position 
corresponding  to  the  axil  of  the  leaf. 

It  will  be  understood  that  in  this  diagram  the  parts 
are  all  represented  on  a  ground-plan,  but  that  as  the 
bud  opens  the  inner  leaves  and  stipules  are  on  higher 
levels  than  the  outer  scales.  In  fact,  proceeding  in  the 
order  of  the  numerals,  we  pass  in  an  ascending  spiral 
from  the  outermost  lower  pair  (1)  of  scales  (stipules)  to 
the  innermost  upper  pair  (21)  with  their  leaf. 

If  we  suppose  the  female  inflorescences  removed,  the 


128  THE   OAK. 

above  diagram  will  serve  to  represent  the  lateral  buds 
which  develop  male  inflorescences  only,  or  if  we  suppose 
the  three  bracts  F,  a,  and  /3  away,  it  would  serve  for  a 
terminal  bud. 

Each  single  female  flower  stands  in  the  axil  of  a 
minute  scale  on  the  floral  axis,  as  said,  and  its  general 
structure  has  been  described.  When  the  pollen  grains 
have  been  dusted  on  to  the  trifid  stigma,  about  the  end 
of  May  or  beginning  of  June,  each  grain  germinates  and 
sends  a  minute  tube  down  the  style,  and  this  pollen-tube 
soon  reaches  the  cavity  of  the  ovary,  and  its  end  becomes 
applied  to  one  of  the  ovules.  While  the  pollen-tube  is 
descending  the  style,  the  ovules  have  arisen  as  minute 
cellular  outgrowths  from  the  angles  of  the  three  cham- 
bers of  the  ovary  (Fig.  34,  d).  There  are  two  in  each 
chamber.  Each  ovule  is  at  first  a  mere  solid  lump  of 
cells  (nucellus),  which  curves  and  becomes  enveloped  in 
two  thin  investing  layers,  called  integuments,  as  shown 
in  the  figures  A-D  (in  Fig.  35).  Inside  the  solid  nucellus, 
n,  of  the  ovule  there  soon  arises  a  small  cavity  filled  with 
nucleated  protoplasm,  and  termed  the  embryo-sac,  e,  be- 
cause the  embryo  is  to  be  developed  in  it. 

This  embryo-sac  contains,  among  other  structures,  a 
minute,  nucleated,  naked  mass  of  protoplasm,  called  the 
oosphore,  or  egg-cell.  The  pollen-tube  has  carried  down 
in  its  apex  also  a  nucleated  mass  of  protoplasm,  and  it 
passes  this  over  into  the  egg-cell  in  the  embryo-sac  ;  the 
union  of  the  nucleus  from  the  pollen-tube  with  the 
nucleus  of  the  egg-cell  constitutes  the  act  of  fertiliza- 


INFLORESCENCE  AND  FLOWERS— FRUIT  AND  SEED.    129 

tion,  and  the  fertilized    egg-cell    is  now  termed   the 
oospore,  and  at  once  begins  to  grow  into  the  embryo. 


FIG.  35. — Various  stages  in  the  development  of  the  ovule  :  w,  nucellus ; 
*',  *',  integuments ;  p,  point  of  attachment  to  placenta ;  c,  embryo-sac ; 
r,  vascular  cord  supplying  ovule;  m,  micropyle;  x,  young  embryo. 
(Partly  after  Th.  Hartig.) 

It  would  be  very  interesting  to  describe  at  length  all 
the  remarkable  details  of   these  processes,  and   their 


130  THE   OAK. 

morphological  meaning  in  the  light  of  modern  biology, 
but  the  limits  and  purpose  of  this  little  book  will  not 
admit  of  that,  and  I  must  content  myself  with  this  brief 
resume. 

During  this  process  of  fertilization  the  cupule  has 
grown  up  like  a  scaly  wall  round  the  ovary  (Fig.  34),  and 
the  tip  of  the  latter  is  seen  peeping  out  from  its  orifice. 

We  are  now  in  a  position  to  understand  generally 
the  changes  that  convert  the  female  flower  into  the 
cupped  acorn  The  fertilized  oospore  becomes  the  em- 
bryo (Fig.  35,  x)  ;  it  grows  at  the  expense  of  the  con- 
tents of  the  embryo-sac,  and  develops  a  radicle,  a  plu- 
mule, and  two  relatively  large  cotyledons,  which  soon 
become  so  big  that  they  occupy  the  whole  space  in  the 
sac  (Fig.  36).  Moreover,  the  embryo-sac  increases  to 
make  more  room  for  this  growing  embryo.  And  now 
comes  in  a  curious  point.  We  saw  that  the  ovary  con- 
sisted of  three  chambers,  each  containing  two  ovules ; 
each  of  these  six  ovules  also  had  its  embryo-sac,  contain- 
ing an  egg-cell,  etc.,  and  each  of  the  total  of  six  egg- 
cells  may  be  fertilized  by  the  contents  of  so  many  pollen- 
tubes  coming  from  pollen  grains  on  the  stigmas.  But 
the  rule  is  that  five  of  the  ovules  with  their  contents 
perish  at  an  early  period,  because  one  strong  one  takes 
the  lead  in  development,  and  starves  the  rest  by  taking 
all  the  available  nourishment  to  itself.  Consequently 
the  advancing  ovary  is  soon  filled  by  one  ovule— the 
other  five  and  two  of  the  chambers  being  pressed  to  one 
side  by  it. 


INFLORESCENCE  AND  FLOWERS— FRUIT  AND  SEED.    131 

In  a  few  weeks  the  ovary  and  its  cupule  have  in- 
creased considerably  in  size,  and  the  one  successful 
ovule,  with  the  rapidly  developing  embryo  in  the  em- 
bryo-sac in  its  interior,  occupies  nearly  the  whole  of  its 
cavity;  the  remains  of  the  two  aborted  chambers  and 


Fio.  36.— Sections  of  acorns  in  three  planes  at  right  angles  to  one  another 
A.  transverse  ;  B,  longitudinal  in  the  plane  of  the  cotyledons  (F) ;  C? 
longitudinal  across  the  plane  of  the  cotyledons ;  c,  cotyledons ;  t, 
testa ;  p,  pericarp ;  «,  scar,  and  r,  radicle ;  pi,  plumule.  The  radicle, 
plumule,  and  cotyledons  together  constitute  the  embryo.  The  em- 
bryonic tissue  is  at  r  and  pi.  The  dots  in  A,  and  the  delicate  veins 
in  B  and  C,  are  the  vascular  bundles. 

the  five  unsuccessful  ovules  being  traceable  as  tiny, 
shriveled  remnants  in  one  corner.  The  walls  of  the 
ovary  then  gradually  change  into  the  polished  brown 
walls  (pericarp)  of  the  fruit ;  the  walls  of  the  ovule  be- 
come the  coat  (testa)  of  the  seed  ;  and  the  embryo  de- 
veloped from  the  fertilized  egg-cell  fills  up  the  interior 
of  the  latter,  as  described  in  Chapter  II. 

The  ripe  fruit  is  the  acorn,  and  we  may  regard  it 
apart  from  the  cupule  ;  it  contains  the  seed. 


132  THE   OAK. 

The  acorn  is  an  egg-shaped,  nut-like  fruit  (ylans}, 
about  18  mm.  long  and  8-10  mm.  broad  (Fig.  3G) ;  the 
apex  is  somewhat  pointed  with  a  hard  remnant  of  the 
stigma,  the  base  is  broader,  and  marked  with  the  cir- 
cular scar  which  denotes  where  it  was  inserted  in  the 
cupule.  The  trifid  character  of  the  stigma  can  often  be 
observed  even  on  the  ripe  fruit,  which  is  smooth  (or 
with  fine  longitudinal  striae),  and  olive-brown  in  color 
when  ripe.  The  ripe  acorn  may  thus  be  regarded  as 
consisting  of  the  pericarp  (to  which  the  calyx  or  peri- 
anth is  fused)  and  the  seed. 

The  pericarp  (Fig.  36,  p)  is  a  thin,  hard  shell,  com- 
prised of  four  layers :  (1)  An  epidermis  of  small,  cuboidal 
cells  with  their  external  walls  much  thickened  (Fig.  37, 
E).  (2)  Four  or  five  series  of  very  thick-walled  and 
pitted  sclerenchyma  cells  (Fig.  37,  1).  (3)  Then  follow 
numerous  rows  of  thin-walled  parenchyma  cells,  com- 
prising the  chief  thickness  of  the  pericarp  (Fig.  37).  It 
is  in  this  tissue  that  the  small  vascular  bundles  supply- 
ing the  pericarp  run,  and  here  and  there  nests  of  scleren- 
chyma cells  are  scattered.  The  parenchyma  cells  may 
contain  minute  starch  grains,  in  addition  to  the  remains 
of  chlorophyll  corpuscles,  even  when  ripe ;  they  also 
contain  tannin,  and,  here  and  there,  crystals  of  calcium 
oxalate.  (4)  The  internal  epidermis  consists  of  elon- 
gated cells  in  one  layer. 

The  seed  proper  fills  up  the  entire  cavity  inclosed  by 
the  fruit- wall  above  described.  It  consists  of  a  relatively 
very  thin  testa,  or  seed-coat,  closely  enveloping  the  large, 


INFLORESCENCE  AND  FLOWERS— FRUIT  AND  SEED.    133 

nr 


FIG.  37.— Transverse  sections  of  the  pericarp  (III)  and  seed  (VI)  of  the 
oak ;  E,  epidermis ;  »,  thick  layer  of  sclerenchyma ;  under  this  come 
the  parenchyma  cells,  with  a  few  sclerenchyma  cells  here  and  there. 
T,  testa  of  seed ;  G,  vascular  bundles ;  e,  the  outer  layer  or  epidermis 
of  the  cotyledon  ;  Co,  thin-walled  cells  of  cotyledons  (of.  Figs.  35  and 
36)  filled  with  starch,  etc.  (Harz.) 
10 


134  THE   OAK. 

straight  embryo  (Fig.  36,  i).  At  the  broad  end  the  fu- 
nicle  can  be  observed  attaching  the  seed  to  the  base  of 
the  acorn;  it  is  inserted  laterally,  and  traces  of  the 
aborted  ovules  may  sometimes  be  found  at  the  point  of 
insertion.  The  vessels  from  the  funiculus  branca  at 
the  chalaza  and  ramify  in  the  testa. 

The  testa  is  a  shining,  pale-brown  or  yellowish  skin, 
consisting  only  of  a  few  rows  of  cuboidal,  thin-walled 
parenchyma  cells,  the  outer  rows  of  which  may  be  the 
integuments,  and  the  innermost  possibly  belong  to  the 
remains  of  the  nucellus ;  or  the  latter  may  be  repre- 
sented by  the  outer  portion  of  the  thin  membrane  which 
includes  all  that  remains  of  the  embryo-sac.  A  few 
feeble  vascular  bundles  run  through  the  testa  (Fig. 
37,  G). 

The  testa  is  closely  applied  to  the  surface  of  the  two 
stout  cotyledons.  These  fill  up  by  far  the  greater  part 
of  the  space  inclosed  by  the  thin  testa  and  pericarp,  and 
their  shape  is  almost  described  in  saying  that.  Each  is 
a  colorless,  hard,  plano-convex  body,  face  to  face  with 
the  other  by  the  flat  surface  (Fig.  36) ;  a  transverse  sec- 
tion of  the  acorn  shows  each  cotyledon  occupying  half 
the  circle.  At  the  more  pointed  end  of  the  acorn  these 
two  cotyledons  will  be  found  to  be  joined  to  the  very 
small  embryo  (plumule  and  radicle)  by  what  will  on 
germination  lengthen  into  very  short  stalks  (petioles), 
but  which  are  at  present  mere  bridges  of  tissue,  across 
which  minute  vascular  bundles  run  from  the  embryo 
into  the  cotyledons.  If  the  shell-like  investments  de- 


INFLORESCENCE  AND  FLOWERS— FRUIT  AND  SEED.    135 

scribed  above  are  removed  from  the  embryo,  it  is  then 
possible  to  gently  separate  the  cotyledons  and  see  the 
minute  plumule  and  radicle  to  which  they  are  joined 
(Fig.  36)  ;  on  removing  one  cotyledon  the  plumule  will 
be  seen  imbedded  in  a  slight  depression  at  the  base.  At 
this  point  there  is  a  little  room  to  spare,  not  quite  filled 
up  by  the  radicle  and  plumule ;  a  minute  remnant  of 
endosperm  may  occasionally  be  found  here,  not  having 
been  entirely  absorbed  by  the  developing  embryo. 

The  cotyledons  and  embryo  are  composed  of  a  deli- 
cate epidermis  inclosing  the  whole  (Fig.  37,  e),  and  very 
thin-walled  cells  forming  the  main  mass  of  tissue  in 
which  the  vascular  bundles  run.  These  bundles  are 
scattered  in  the  thickness  of  the  cotyledons,  ready  to 
convey  fluids  to  and  fro  on  germination,  and  already 
contain  lignified  vessels  in  the  xylem  and  sieve-tubes  in 
the  phloem. 

The  iso-diametric,  closely-packed  cells  of  the  cotyle- 
dons are  filled  with  reserve  materials,  consisting  of  large 
quantities  of  starch  grains  imbedded  in  proteids  and 
tannin.  Here  and  there  are  scattered  cells  filled  with 
brown  pigments  and  containing  tannin ;  some  cells  also 
contain  oil-drops.  Traces  of  sugar  (quercite),  certain 
bitter  principles,  acids,  and  mineral  substances  also  occur 
in  the  tissues. 


CHAPTER  X. 

OAK   TIMBER — ITS  STRUCTURE   AND   TECHNOLOGICAL 
PECULIARITIES. 

IT  is  now  time  to  look  at  the  timber  of  the  oak  as  a 
material,  and  to  examine  its  technical  properties  from 
the  various  points  of  view  of  those  who  employ  such 
material.  Oak  timber  may  be  described  as  follows  : 

(1)  Appearance  and  Structure. — Pith  pentangular, 
1  to  4  mm.  diameter,  whitish  at  first,  and  then  browner, 
formed  of  small,  thick-walled  cells. 

Sap-wood  narrow  and  yellowish-white ;  heart-wood 
varies  in  shades  of  grayish  or  yellow  brown  (fawn  color) 
to  reddish  or  very  dark  brown.  It  darkens  on  exposure, 
and  works  to  a  glossy  surface  if  healthy. 

Annual  rings  well  marked  by  the  one  to  four  lines  of 
large  vessels  in  the  spring  wood,  whence  radiate  outward 
tongue-like  and  branched  groups  of  smaller  and  smaller 
vessels,  tracheids,  and  cells,  in  a  groundwork  of  darker 
fibers.  Indistinct  peripheral  lines  of  parenchyma  are 
also  visible,  especially  in  the  broader  annual  rings.  The 
annual  rings  are  slightly  undulating,  bending  outward 
between  the  large  medullary  rays  (Fig.  38). 


OAK   TIMBER. 


137 


Medullary  rays  of  two  kinds,  a  smaller  number  of 
very  broad,  shining  ones,  from  £  to  1  mm.,  or  even  a 
centimetre  or  more  apart,  and  very  numerous  (about 


FIG.  38. — Transverse  section  of  wood  of  oak  (magnified  live  diameters), 
showing  five  annual  rings,  as  denoted  by  the  large  vessels  of  the 
spring  wood ;  the  vessels  become  smaller  in  the  summer  and  autumn 
wood,  and  are  arranged  in  tongue-like  groups.  Nine  broad  medullary 
rays  are  shown,  the  rest  are  very  narrow  (cf.  Fig.  27).  The  rest  of 
the  section  is  filled  with  tracheids,  fibers,  and  wood-parenchyma. 
(MUller.) 


138  THE   OAK 

twelve  per  mm.)  fine  ones  between  them,  which  undu- 
late between  the  vessels.  In  slowly-grown  close  wood 
there  is  no  vestige  of  radial  arrangement  left. 

In  the  tangential  section  the  small  medullary  rays  are 
seen  to  consist  each  of  a  vertical  row  of  a  few  cells,  the 
large  ones  having  numerous  cells  (see  Fig.  27). 

Wood-parenchyma  cells  broader  than  small  medullary 
rays,  and  the  color  is  chiefly  due  to  pigment  in  these 
wood-  and  ray-cells.  The  wood-cells  are  pitted  with  ob- 
lique, slit-shaped,  simple  pits. 

The  vessels  have  bordered  pits,  and  the  septa  are  per- 
forated each  by  one  large  circular  opening.  The  smaller 
vessels  have  delicate  spirals  on  their  walls  as  well  as  bor- 
dered pits. 

Nordlinger  says  that  pith-flecks  occur  occasionally. 

It  is  impossible  to  distinguish  between  the  \vood  of 
the  varieties  pedunculata  and  sessiliflora. 

(2)  Its  density  varies  considerably.  Taking  the 
weight  of  a  given  volume  of  water  as  unity,  the  weight 
of  an  equal  volume  of  oak  timber  may  weigh  from  0*633 
when  air-dry  to  T280  when  fresh  cut.  We  may  take  the 
average  density  of  green — i.  e.,  newly-felled — oak  with 
all  its  sap  present,  as  about  1-075,  and  that  of  the  sea- 
soned wood  as  about  0*78. 

It  must  be  borne  in  mind,  however,  that  these  weights 
refer  to  the  wood  as  a  structure — that  is,  a  complex  of 
vessels  and  cells,  etc.,  containing  air  and  liquids — and  do 
not  give  the  specific  gravity  of  the  wood  substance  itself. 
The  latter  may  be  obtained  by  driving  off  all  the  air  and 


OAK   TIMBER.  139 

water  from  the  wood,  and  is  found  to  be  1-56,  compared 
with  an  equal  volume  of  water  taken  as  unity.  It  is  the 
varying  quantities  of  this  wood  substance,  and  of  air  and 
water  in  the  cavities,  which  make  the  density  of  different 
pieces  of  oak  vary  so  much. 

(3)  The  proportion  of  sap  contained  in  the  cavities 
of  the  vessels,  cells,  etc.,  of  course  differs  at  different 
times.     In  the  spring,  just  as  the  buds  are  opening,  the 
quantity  of  water  increases  more  and  more  up  to  about 
July,  when  the  maximum  is  attained ;  the  proportion 
of  water  to  solids  then  sinks  until  October,  when  the 
leaves  fall ;  it  increases  again  up  to  Christmas-tide,  and 
then  sinks  to  the  minimum  in  the  coldest  part  of  the 
winter.     The  proportion  of  water  to  the  total  weight  of 
the  felled  wood  may  vary  from  22  to  39  per  cent. 

(4)  Obviously  the  loss  of  water  on  drying  causes 
shrinkage  of  the  wood,  and  although  oak  shrinks  very 
little  in  the  direction  of  its  length  (0-028  to  0-435  per 
cent),  the  effect  is  very  marked  in  other  directions.     In 
the  radial  direction — i.  e.,  in  the  direction  of  the  medul- 
lary rays — it  may  shrink  from  1  to  7'5  per  cent  of  its 
measurement  when  first  felled ;  and  in  the  direction 
vertical  to  this — i.  e.,  parallel  to  a  tangent  to  the  cylin- 
drical stem — the  variation  is  from  0-8  to  10-6  per  cent. 
Of  course,  green  oak  shrinks  much  more  than  seasoned 
and  older  wood,  the  process  of  seasoning  being,  in  point 
of  fact,  the  period  of  chief  shrinkage.     It  is  said  that 
wood  from  the  variety  sessiliflora  shrinks  more  than 
that  of  the  variety  pedunculata,  but  it  may  be  doubted 


140  THE  OAK. 

how  far  the  difference  would  hold  if  sufficiently  numer- 
ous comparisons  were  made. 

(5)  Swelling  may  be  regarded  as  complementary  to 
shrinkage.     It  has  been  found   that  if  oak  wood  is 
allowed  to  absorb  water  until  thoroughly  saturated  it 
will  increase  from  0-13  to  0-4  per  cent  in  length,  and 
be  distended  radially  from  2-66  to  3-9  per  cent,  or  tan- 
gentially  5*59  to  7'55  per  cent,  according  to  age  and 
condition,  young  wood  swelling  more  than  old.     It  has 
also  been  found  that  the  total  volume  increased  from 
5-5  to  7-9  per  cent,  and  the  weight  from  60  to  91  per 
cent,  on  complete  saturation. 

(6)  Elasticity  and  Tenacity. — Oak  is  very  elastic, 
and  easily  bent  if  steamed,  and   it  does  not  readily 
splinter.     When  pulled  in  a  direction  parallel  to  the 
length  of  the  structure  the  absolute  tenacity  =  2 '23  to 
14-51  kgr. — i.  e.,  it  took  a  pull  equal  to  this  weight  per 
1  sq.  mm.  of  section  to  pull  the  wood  asunder. 

The  limit  of  elasticity  corresponds  to  a  load  of  2 '72 
to  3-5  kgr.,  according  to  various  authorities,  the  speci- 
men lengthening  ^j-th  in  the  former  case. 

The  modulus  of  elasticity  is  given  as  826  to  1,030 
kgr.,  and  the  breaking  limit  as  4-66  to  6-85. 

When  the  pull  is  in  a  direction  across  the  length  of 
the  fibers,  the  results  differ  according  as  the  load  is 
applied  so  as  to  act  radially  or  tangentially. 

When  acting  radially  the  modulus  of  elasticity  is 
given  as  188-7  kgr.,  and  the  breaking  limit  as  0-582  kgr. 

When  acting  parallel  to  a  tangent  the  modulus  of 


OAK   TIMBER.  141 

elasticity  =  129-8  kgr.,  and  the  breaking  limit  0-406 
kgr. 

The  absolute  tenacity  in  the  transverse  direction  is 
given  as  0-44  to  0-61  kgr. 

In  the  case  where  pressures  are  applied  in  the  direc- 
tion of  the  length  of  the  fibers  the  limit  of  elasticity  = 
2-09  to  2-22  kgr. ;  the  modulus  of  elasticity,  933  to  1,250 
kgr. ;  and  the  absolute  resistance,  2-58  to  3-64  kgr. 

Flexibility. — The  limit  of  elasticity  =  1'77  to  2*71 
kgr. ;  modulus  of  elasticity,  620  to  735  kgr. ;  resistance 
to  bending,  4-53  to  6-18  kgr. 

Torsion. — Oak  warps  considerably  unless  carefully 
seasoned.  Limit  of  elasticity  =  0-4  to  0-54  kgr. ;  modu- 
lus of  elasticity,  612*5  to  785  kgr. ;  resistance  to  torsion, 
0-75  to  0-97  kgr. 

Eesistance  to  shearing- stress,  in  the  direction  of  the 
fibers  =  0-61  to  0*97  kgr. ;  perpendicular  to  them,  1-9 
to  3-49  kgr. 

(7)  Resistance  to  Splitting. — Oak  is  easily  split  into 
tolerably  smooth  and  even  staves,  and  is  much  employed 
for  this  purpose. 

(8)  Hardness. — Oak  is  neither  the  hardest  and  heavi- 
est nor  the  most  supple  and  toughest  of  woods,  but  it 
combines  in  a  useful  manner  the  average  of  these  quali- 
ties.    Good  oak  is  hard,  firm,  and  compact,  and  with  a 
glossy  surface,  and  varies  much ;  young  oak  is  often 
tougher,  more  cross-grained,  and  harder  to  work  than 
older  wood.     According  to  Gayer,  if  we  call  the  resist- 
ance which  the  beech  offers  to  the  saw,  applied  trans- 


14:2  THE 

verse  to  the  fibers,  1,  then  that  of  freshly  felled  oak 
=  1-09. 

(9)  Durability. — A  mild  climate  and  open  situation 
produces  the  most  durable  oak,  and  it  is  extraordinarily 
durable  under  water,  in  the  earth,  or  exposed  to  wind 
and  weather,  or  under  shelter ;  in  the  latter  case  it  be- 
comes more  and  more  brittle  as  years  roll  by. 

The  alburnum  becomes  rotten  Usually  in  a  few  years 
if  exposed,  and  is  the  prey  of  insects  if  under  cover. 
The  heart,  if  sound,  may  last  for  centuries  under  cover 
and  well  ventilated,  and  even  in  earth  or  water  will 
endure  for  several  generations.  There  are,  for  instance, 
in  the  museum  at  Kew,  a  portion  of  a  pile  from  old 
London  Bridge  which  was  taken  up  in  1827,  after  hav- 
ing been  in  use  for  about  650  years,  and  a  piece  of  a 
beam  from  the  Tower  of  London,  of  which  it  is  stated 
that  it  was  "  probably  coeval  with  the  building  of  the 
Tower  by  William  Ruf  us  " ;  and  many  other  specimens 
of  very  old  oak  are  known. 

(10)  Burning  Properties. — The  calorific  power  of 
oak  wood  is  high,  in  accordance  with  its  density,  but  it 
splutters  and  crackles  and  blackens  too  much.     Never- 
theless, it  produces  a  valuable  charcoal.      Hartig  says 
that  if  we  call  the  cooking-power  of  a  given  volume  of 
beech  1,  that  of  an  equal  volume  of  oak  =  0*92  to  0-96. 

(11)  Peculiarities. — Oak  timber  is  apt  to  suffer  from 
various  diseases,  and  from  frost-cracks  and  star-shakes, 
cup-shakes,  etc.,  as  we  shall  see  in  the  next  chapter.     It 
often  presents  brittle  wood,  red-rot  (foxiness),  white-rot, 


OAK   TIMBER.  143 

spottiness  of  various  kinds,  and  is  sometimes  twisted. 
At  the  roots  it  is  very  often  affected  with  burrs.  It  con- 
tains gallic  acid,  and  so  corrodes  iron  nails,  clamps,  etc. 

(12)  Uses. — Owing  to  its  high  price  and  great  spe- 
cific weight,  oak  has  suffered  in  competition  with  spruce, 
larch,  and  pine  so  far  as  building  is  concerned ;  but  its 
uses  are  very  various  and  widespread  nevertheless,  and 
it  is  invaluable  to  the  engineer  and  builder  wherever 
strength  and  durability  are  aimed  at. 

As  already  said,  its  great  value  depends  on  its  mar- 
velous combinations  of  several  average  properties ;  and 
considerable  variations  in  the  density,  durability,  ease 
of  working,  and  beauty  when  worked,  and  so  forth,  are 
met  with  according  to  the  situation  and  climate  in  which 
the  oak  grows.  Generally  speaking,  it  is  found  that 
when  the  oak  grows  isolated  in  plains,  in  rich  soil  and  a 
mild  climate  (habitat  of  Q.  pedunculata),  it  grows  rap- 
idly, and  produces  a  wood  of  very  tough  and  horny  con- 
sistency, which  is  regarded  as  the  best  for  naval  and 
hydraulic  work,  cartwrights,  etc.,  and  wherever  strength, 
tenacity,  and  solidity  are  required  in  high  degree  (Fig. 
39,  top).  The  best  should  have  broad  and  equal  rings, 
but  not  broader  than  7  to  8  mm.,  with  narrow  vascular 
zone  and  the  smallest  possible  vessels,  and  with  a  pale, 
rather  than  dark,  and  even  color  on  the  fresh  section. 
It  should  also  have  long  fibers  and  a  strong,  fresh  smell. 

In  close,  high  forest,  on  poor  soil,  and  in  a  rougher 
climate,  it  may  take  300  years  to  reach  0'6  metre  diame- 
ter, and  the  wood  is  then  softer  and  more  porous,  beau- 


144 


THE   OAK. 


HHH 
I 


FIG.  39. — Three  specimens  of  oak  grown  under  different  conditions. 


OAK   TIMBER.  145 

tifully  speckled,  and  shrinking  little  (Fig.  39,  middle). 
Such  wood  is  excellent  for  sculpture  and  carving,  and 
is  very  pretty ;  it  is  also  well  adapted  for  cooperage. 

In  deep  soil  of  moderate  quality,  in  hilly  country, 
and  growing  as  coppice  under  standards,  we  have  a 
wood  of  irregular  growth  and  not  very  valuable,  but 
useful  in  an  all-round  way  for  sawing  and  splitting  (Fig. 
39,  bottom). 

Speaking  generally,  it  is  found  that,  other  things 
being  equal,  the  most  resistant,  closest,  and  toughest 
timber  comes  from  isolated  trees  growing  in  the  open  : 
straight  and  long  timber,  less  marked  for  the  above 
qualities,  comes,  on  the  contrary,  from  trees  grown  in 
close,  high  forest.  This  is  the  conclusion  arrived  at  by 
the  naval  authorities  in  France  and  England,  and  may 
be  accepted  as  according  with  the  facts  of  structure,  etc. 
Some  differences  may  be  put  down  to  the  varieties,  but 
probably  Boppe  is  right  in  concluding  that  rate  of 
growth,  etc.,  due  to  differences  in  the  soil  and  climate, 
are  the  determining  causes. 

The  builder  employs  oak  for  sills,  staircase  treads, 


DESCRIPTION  OF  FIG.  39. — The  upper  one  is  from  a  rapidly-grown 
tree,  in  the  open,  and  at  a  low  altitude  ;  the  wood  is  very  strong,  hard, 
and  heavy  (density  OS27),  because  there  is  a  preponderance  of  fibers  in 
the  broad  rings.  The  middle  specimen  comes  from  a  tree  growing  slowly 
in  a  forest  at  a  considerable  altitude  ;  the  narrow  rings  have  too  large  a 
proportion  of  vessels,  whence  the  wood  is  soft  (density  O691),  porous, 
and  weak.  The  lower  section  is  from  a  tree  which  has  grown  very 
irregularly  on  poor  soil,  as  shown  by  the  variable  rings  ;  only  the  parts 
with  broad  rings  are  good — hence  bad  wood  predominates  (density 
0-742).  (Nanquette-Boppe.) 


146  THE  OAK- 

keys,  wedges  and  treenails,  gate-posts  and  doors,  and 
superior  joinery. 

Railway-sleepers  are  best  made  of  young  oak,  as  it 
is  denser,  and  the  Austrians  say  such  sleepers  last  from 
seven  to  ten  years  if  not  treated,  and  for  as  long  as  six- 
teen years  if  treated  with  zinc  chloride  and  other  pre- 
servatives. 

On  the  Continent  heavy  oak  is  used  in  machines,  for 
axletrees,  spokes,  stamps  of  mills,  anvil-stocks,  hammer- 
handles,  etc. 

Oak  is  much  used  for  carving  of  all  kinds,  large  fur- 
niture, paneling,  parquetry,  for  the  felloes,  spokes,  and 
axles  of  wheels,  and  for  other  parts  of  wagons,  etc.  In 
cooperage  it  is  much  used  for  the  staves,  etc.,  of  casks, 
measures,  sieves. 

Split  oak  makes  excellent  palings  and  shingles,  and 
oak  vine-props  are  only  second  to  those  of  chestnut. 
Walking-sticks  are  also  made  of  oak,  and  even  water- 
pipes  have  been  used,  but  they  taint  the  water. 


CHAPTER  XL 

THE    CULTIVATION"   OF   THE    OAK,    AND   THE    DISEASES 
AND   INJURIES   TO    WHICH    IT   IS   SUBJECT. 

THE  oak  has  been  cultivated  in  all  kinds  of  ways, 
but  by  far  the  best  timber  is  produced  in  what  is  called 
"  high  forest " — that  is,  the  young  trees  all  start  at  the 
same  age  and  planted  much  closer  together  than  they 
will  be  later  on,  their  number  being  lessened  period 
after  period  by  successive  removals  until  there  is  left  a 
forest  of  large  trees  at  equal  distances.  As  it  takes 
from  140  to  200  years  to  bring  such  a  crop  of  timber  to 
maturity,  we  may  easily  understand  that  such  are  rarely 
met  with  except  as  State  forests,  and  the  governments 
of  various  countries  keep  them  going  at  various  ages : 
one  set  of  plantations  will  be  ten,  another  twenty,  a 
third  thirty  years  old,  for  instance,  when  a  given  set  is 
ready  to  be  finally  cut  over  for  heavy  timber. 

There  are  many  difficulties,  however,  in  cultivating 
pure  oak  woods,  and  the  custom  of  mixing  other  trees 
is  a  common  one,  for  the  young  oaks  need  much  light ; 
and  yet,  if  each  plant  has  the  space  given  it  necessary  to 
allow  of  this  light,  it  grows  into  a  short  and  spreading 
tree  instead  of  rising  up  into  a  tall,  straight  one.  The 


148  THE  OAK. 

forester  usually  gets  over  these  difficulties  by  planting 
beech,  or  silver  fir,  or  some  other  species  among  the  oaks, 
but  in  such  a  way  that  the  oaks  are  never  completely 
shaded  by  the  other  trees — that  is  to  say,  he  keeps  the 
trees  at  different  ages,  the  beach,  hornbeam,  silver  fir, 
spruce,  etc.,  only  being  allowed  to  just  close  in  the  forest, 
leaving  the  leaf -crowns  of  the  oaks  to  be  fully  exposed  to 
the  light  above.  The  oak  grows  faster  than  the  beech 
or  spruce,  for  instance,  while  young,  and  so  keeps  its 
head  easily  above  the  others  for  a  time.  Very  often  the 
oak  is  cultivated  pure  at  first,  and  then,  when  the  oaks 
are  becoming  too  crowded  and  he  has  to  thin  them,  the 
forester  puts  in  the  silver  fir  or  beech,  which  prevents 
the  light  coming  in  to  the  lower  parts  of  the  young  oak- 
trees,  and  consequently  prevents  the  development  of 
lower  branches,  which  would  give  the  spreading,  squat 
habit  he  wishes  to  prevent.  For  without  light  the 
leaves  of  the  lower  twigs  of  course  can  not  make  the 
materials  to  strengthen  and  thicken  the  latter  into 
branches,  and  so  they  die  off,  and  the  trunk  remains  a 
straight,  clean  cylinder. 

Although  oaks  are  often  raised  from  seed,  a  number 
of  veteran  trees  being  allowed  to  stand  for  many  years 
in  order  to  scatter  the  acorns,  yet  in  by  far  the  greater 
number  of  cases  the  plants  are  put  in  artificially,  the 
long  tap-roots  being  first  cut  in  order  to  make  them 
throw  out  lateral  rootlets.  It  is  also  a  common  practice 
to  cut  back  oaks,  and  allow  them  to  sprout  into  what  is 
known  as  coppice— that  is  to  say,  numerous  buds  which 


THE   CULTIVATION   OF  THE   OAK.  149 

would  not  have  developed  at  all  are  impelled  to  grow 
up  into  twigs  and  branches  (stool-shoots)  from  the  lower 
parts  of  the  cut  tree.  It  was  very  usual  at  one  time  to 
grow  oak  in  this  way  for  the  sake  of  the  bark,  which 
was  employed  in  tanning,  the  trees  being  cut  back  again 
and  again,  and  renewing  the  coppice  growth  after  each 
cutting. 

There  are  various  other  modes  of  growing  oak  in 
forests,  but,  whatever  the  system  employed,  the  follow- 
ing facts  have  to  be  borne  in  mind  and  provided  for : 
The  oak  is  a  tree  that  requires  a  soil  of  great  depth,  and 
sufficiently  open  to  allow  of  the  free  penetration  of  air 
and  water  to  the  subsoil ;  consequently  many  soils,  other- 
wise rich  enough,  are  unsuited  for  the  culture  of  this 
tree.  Again,  young  seedlings  and  plants  are  apt  to 
suffer  from  frost  unless  they  are  protected  by  suitable 
mixtures  of  other  plants;  but  such  mixtures  must  be 
chosen  properly,  for  this  tree  demands  light  and  space 
to  a  degree  greater  than  most  other  European  trees  ex- 
cept the  larch,  birch,  and  one  or  two  others,  and  rapidly 
suffers  if  shaded  or  unduly  crowded.  Further,  as  com- 
pared with  other  European  trees,  the  oak  is  a  tree  of 
the  plains,  and  requires  a  relatively  high  temperature. 
These  requirements  also  accord  with  its  adaptation  to 
deep,  rich,  well-drained  soil,  and,  taking  it  all  round,  we 
have  to  regard  the  oak  as  a  tree  which  makes  consider- 
able demands  on  the  locality  (soil  and  climate)  where 
it  grows.  In  return  for  this,  however,  it  yields  the 
best  of  all  temperate  timbers. 


150  THE   OAK. 

As  we  have  seen,  the  forester  has  to  exercise  con- 
siderable forethought — the  outcome  of  long  experience 
— in  growing  oak  so  as  to  obtain  long,  clean  stems.  The 
natural  habit  of  the  tree  is  to  form  a  short,  thick  bole 
and  a  widely  spreading  crown,  the  main  branches  of 
which  come  off  not  far  from  the  ground.  To  compel 
the  stem  to  elongate  into  a  long  pole  he  has  to  plant 
other  trees  with  it  (as  we  have  seen,  beech,  spruce,  etc.), 
which,  while  they  keep  the  light  off  the  lower  parts  of 
the  oaks,  do  not  overtop  them.  This  makes  the  trees 
long  and  spindly  at  first,  as  they  run  up  their  leaf- 
crowns  higher  and  higher,  and  it  is  part  of  the  forester's 
art  to  select  the  exact  time  when  he  may  cut  away  some 
of  the  nurse  trees  and  let  in  just  enough,  and  not  too 
much,  light  and  air,  so  that  the  crowns  of  the  oaks  shall 
fill  out  more  and  thicken  the  stems.  For  it  must  never 
be  forgotten  that  the  timber  is  laid  on  from  substance 
prepared  in  the  leaves. 

The  natural  shape,  so  to  put  it,  of  an  oak-tree  is 
that  of  a  wide-spreading,  short-stemmed  mushroom,  and 
such  a  shape  is  realized  in  the  open ;  the  forester  com- 
pels it  to  lengthen  its  stem  as  much  as  possible  before 
he  lets  it  extend  its  crown.  Hence  he  aims  at  length 
first,  and  then  lets  the  tree  put  on  timber  in  the  mass. 
He  does  this,  of  course,  by  taking  advantage  of  the  tree's 
peculiarities,  and  one  of  these  is  that  it  grows  very 
rapidly  when  young.  It  will  be  obvious  that  the  skilled 
forester  also  has  to  aim  at  getting  as  much  timber  as 
possible  on  the  ground  in  a  given  time,  and  in  the  case 


THE   CULTIVATION   OF   THE   OAK.  151 

of  a  tree  like  the  oak  his  calculations  have  to  be  well 
made  beforehand,  for  the  tree  may  have  to  stand  for 
from  120  to  200  years  before  it  is  cut.  Left  alone  it 
may  live  for  1,000  years,  but  the  proportion  of  good 
timber  in  trees  after  a  certain  age  rapidly  diminishes — 
a  fact  that  has  also  to  be  reckoned  with. 

It  is  quite  different,  however,  when  trees  are  re- 
quired for  seed  purposes.  The  oak  hardly  bears  fruit 
at  all  before  it  is  fifty  to  sixty  years  old,  and  seventy 
to  eighty  years  is  a  better  age  for  the  purpose ;  but, 
as  with  other  trees,  to  produce  really  good  seed  the 
oaks  must  be  isolated,  or  nearly  so,  so  that  they  get  the 
maximum  of  light  and  air.  Consequently  a  modifica- 
tion of  procedure  has  to  be  made  when  seed-trees  are 
required. 

When  the  fruiting  period  has  once  been  reached  the 
tree  goes  on  producing  acorns  every  year ;  but  it  is  noticed 
that  heavy  crops  of  good  seeds  only  recur  every  five  (or 
perhaps  three)  years  or  so,  the  yield  in  the  intervals  be- 
ing inconsiderable.  This  is  in  accordance  with  Hartig's 
discovery  that  in  the  beech,  for  instance,  the  tree  goes 
011  storing  up  nitrogenous  materials  and  salts  of  phos- 
phorus and  potassium  during  the  first  seventy  or  eighty 
years  of  its  life,  and  then  suddenly  yields  these  stores  to 
the  seeds;  the  drain  is  so  exhausting  that  it  requires 
three  to  five  years  to  re-store  sufficient  of  these  sub- 
stances for  another  "  seed-year."  The  season  or  weather 
is  also  concerned  in  the  matter. 

Of  course  there  are  very  many  other  details  to  be 


152  THE  OAK. 

considered  in  the  technical  cultivation  of  the  oak,  but 
enough  has  been  said  to  give  the  reader  a  general  ac- 
count of  the  procedure,  and  I  now  pass  to  the  subject  of 
the  dangers  and  diseases  which  threaten  the  tree  at 
various  periods  in  its  development,  and  the  timber 
afterwards. 

The  diseases  and  injuries  to  which  the  oak  is  subject 
are  very  numerous  and  various,  although,  compared  with 
some  other  indigenous  trees,  it  suffers  remarkably  little 
from  the  different  dangers  which  await  it  at  all  stages 
in  the  course  of  its  long  life  from  the  seedling  to  the 
aged  tree.  Some  of  these  are  referable  to  the  exigencies 
of  the  non-living  environments — the  climate,  soil,  ete. ; 
others  are  due  to  the  attacks  of  living  organisms,  both 
vegetable  and  animal — from  the  weeds  which  smother 
the  young  seedlings  by  keeping  the  light  from  them,  to 
man  himself,  who  injures  the  trees  in  various  ways. 
The  earliest  struggles  of  the  young  seedling  are  with 
the  weeds,  slugs,  and  insects  of  various  kinds  that  in- 
vade the  territory  on  which  the  acorn  has  germinated ; 
and  of  course  the  baby  plant  has  also  to  contend  against 
any  inclemencies  of  climate  or  unsuitableness  of  soil 
that  it  may  meet  with.  Owing  to  such  vicissitudes  very 
many  of  the  seedlings  never  obtain  the  dimensions  of  a 
plant  at  all,  and  in  some  seasons  the  mortality  is  enor- 
mous. Other  destructive  agents  during  these  early  phases 
of  the  life  of  the  oak  are  cattle  and  deer,  which  not  only 
tread  down  the  shoots  but  also  nibble  them  off,  and 
mice,  squirrels,  etc.,  do  their  share  of  injury,  as  also  do 


THE  CULTIVATION  OF  THE  OAK.  153 

wood-pigeons  and  other  birds.  In  the  north  of  Europe 
the  young  plants  suffer  terribly  from  the  ravages  of  a 
fungus  named  Rosellinia,  the  mycelium  of  which  sends 
its  branches  into  the  roots  and  kills  them,  consequently 
entailing  the  death  of  the  plant.  The  larvae  of  various 
insects  also  damage  the  roots  and  bring  about  injuries 
which  may  prove  fatal.  Cynips  corticalis  produces  galls 
on  the  lower  parts  of  the  stems. 

When  the  plant  has  passed  into  the  condition  of  a 
sapling  its  dangers  are  for  the  most  part  of  quite  other 
nature,  the  injurious  fungi  especially  being  different. 
The  chief  diseases  of  the  roots  now  arise  from  their 
spreading  into  unsuitable  soil,  the  drainage  of  which 
may  be  incomplete,  and  thus  bring  about  a  sodden,  acid, 
ill-aerated  condition.  The  want  of  oxygen  and  the  low 
temperature  combine  to  kill  the  root- hairs  and  young 
rootlets,  and  the  leaves  above  part  with  their  water 
faster  than  it  can  be  supplied  from  below,  and  they 
turn  yellow  and  die  off,  the  branches  dry  up,  and  the 
tree  dies. 

Other  dangers  arise  from  the  persistent  overshadow- 
ing of  other  trees,  which  slowly  kill  the  young  oaks  by 
depriving  their  leaves  of  light ;  the  offending  trees 
playing  the  same  inimical  part,  in  fact,  that  grass  and 
weeds,  etc.,  play  towards  the  small  seedlings.  Or  the 
roots  may  be  too  thickly  set  in  the  soil  if  the  trees  are 
too  crowded,  and  each  suffers  from  over-competition 
with  others. 

Much  mischief  is  effected  by  the  attacks  of  insects 


154  THE   OAK. 

of  various  kinds.  The  caterpillars  of  certain  moths 
(especially  Cnethocampa  and  Tortrix),  for  instance,  eat 
off  the  leaves  in  June,  and  then  form  large  masses  of 
mingled  debris,  skins,  etc.,  as  they  pass  into  the  pupa 
stage  in  July.  The  denudation  of  the  leaves  brought 


FIG.  40.—  Tortrix  viridana,  the  preen  oak-moth,  the  larvae  of  which  eat 
off  the  young  leaves.    ( Altum.) 

about  by  such  caterpillars  is  apt  to  be  very  exhaustive 
to  the  trees,  for  although  they  put  forth  new  foliage  in 
July  and  August,  it  must  not  be  forgotten  that  these 
new  leaves  are  constructed  from  materials  which  should 
have  gone  to  the  general  stores  in  the  tree,  and  from 
which  new  wood,  for  instance,  would  have  been  devel- 
oped. 


THE  CULTIVATION  OF  THE   OAK.  155 

Of  other  animals  which  injure  oaks  I  may  mention 
the  various  cattle,  which  bite  off  or  rub  the  bark  and 
buds ;  hares,  squirrels,  mice,  etc.,  which  nibble  roots  and 
buds  and  destroy  the  acorns,  etc. ;  and  a  few  birds ;  and 
certain  beetles,  which  bore  into  the  wood. 

Among  the  pests  belonging  to  the  vegetable  kingdom 
the  following  may  be  selected  from  a  large  number : 
The  honeysuckle  occasionally  twists  tightly  round  the 
young  stem,  and  in  course  of  time  so  compresses  the 
cortex  that  the  formative  materials  from  the  leaf-crown 
have  to  pass  in  a  spiral  course  between  the  coils  of  the 
strangling  plant,  and  the  tightly-squeezed  parts  may  be 
starved  as  the  tree  thickens,  and  even  the  death  of  the 
cambium  may  follow,  especially  if  one  or  two  of  the 
honeysuckle  coils  come  to  lie  nearly  horizontally  round 
the  stem. 

As  a  rare  event  the  mistletoe  is  found  on  the  oak. 
A  much  commoner  parasite  of  the  same  family  is  Loran- 
tlius  europmis,  which  does  considerable  damage  to  oaks 
in  some  parts  of  Europe.  The  sticky  seeds  are  carried 
into  the  trees  by  thrushes.  Here  they  germinate,  and 
send  their  roots,  or  haustorial  strands,  into  the  cortex  of 
a  branch  as  far  as  the  cambium,  where  they  spread  and 
feed  on  the  contents  of  the  young  wood-  and  cambium- 
cells,  causing  malformations  of  the  injured  branch  at 
the  spot  attacked,  owing  to  the  hypertrophy  of  the  tis- 
sues, to  which  abnormal  quantities  of  food  materials 
now  flow  (Fig.  41)  ;  and  frequently  bringing  about  the 
death  of  the  upper  parts  of  the  branches  owing  to  the 


156 


THE  OAK. 


paucity  of  water  at  those  parts,  the  parasite  taking  much 
of  that  which  reaches  the  injured  place,  and  the  impov- 
erished wood  allowing  less  to  pass  than  it  would  normally 
have  done. 

Among  the  fungi  there  are  several  enemies  to  the 
oak-tree.    The  leaves  are  attacked  by  Phyllactinia,  one 


FIG.  41. — Loranthus  europceus.  A.  Lower  part  of  stem  attached  to  branch 
of  oak,  both  denuded  of  cortex.  B.  Longitudinal  section  through  one 
of  the  haustorial  strands,  showing  its  progress  year  by  year,  as  the 
branch  thickens.  C.  Transverse  section,  through  a  branch  which 
has  long  been  badly  infested  with  the  Lo  ran  thus  ;  a  a,  dead  remains 
of  old  haustorial  strands;  b  J,  young  Loranthus  plants  developed  as 
buds  from  the  older  ones.  The  asterisks  mark  still  younger  speci- 
mens. (Ilartig.) 


of  the  mildews,  which  forms  white  networks,  like  spiders' 
webs,  on  their  surfaces.  Numerous  small  ascomycetous 
fungi  are  found  on  the  dying  and  dead  leaves,  but  these 
do  not  directly  injure  the  living  tree. 

Other  fungi  are  found  in  the  cortex,  and  one  of  the 
most  interesting  of  these  is  a  red  Nectria,  the  spores  of 


THE   CULTIVATION   OF   THE   OAK.  157 

which  germinate  on  the  bark,  but  can  not  infect  the  tree 
unless  there  is  a  wound  in  the  neighborhood.  How- 
ever, owing  to  the  numerous  small  cracks  and  ruptures 
due  to  the  injuries  caused  by  insects,  hail,  frost,  etc.,  the 
mycelium  easily  gains  access  to  the  cortex  and  cambium, 
and  feeds  on  the  contents  of  the  cambium-cells,  which 
it  destroys.  The  consequence  of  the  irritations  set  up  is 
the  formation  of  canker-like  knots  on  the  branches,  and 
the  injury  may  be  great  enough  to  destroy  smaller  ones, 
and  occasionally  even  a  large  one. 

Unquestionably  the  most  important  of  the  diseases 
to  which  the  older  oak-trees  are  subject  are  those  which 
result  in  the  destruction  of  the  timber. 

There  are  about  six  or  eight  of  the  fungi  known 
popularly  as  toadstools — technically  as  Hymenomycetes 
— which  are  able  to  injure  and  even  destroy  the  timber 
of  standing  oaks,  and  while  each  of  these  pests  does  the 
damage  in  its  own  peculiar  way,  they  show  considerable 
similarity  in  general  behavior.  In  the  first  place,  these 
fungi  are  unable  to  penetrate  the  bark  of  sound  trees, 
and  their  hyphae  always  gain  access  to  the  timber  by 
means  of  actual  wounds  and  exposed  surfaces  of  wood, 
such  as  the  cracks  caused  by  frost  or  by  the  bending 
down  of  heavy  branches  under  the  weight  of  a  load  of 
snow,  or  the  ruptured  ends  of  broken  branches  blown  off 
by  strong  gales  or  struck  by  falling  trees,  or  places  where 
animals  have  removed  the  bark,  where  cart-wheels  have 
abraded  the  larger  roots,  and  so  on.  Once  inside,  the 
hyphae  of  these  fungi  pierce  the  vessels,  cells,  etc.,  of  the 


158  THE  OAK. 

wood  by  excreting  soluble  ferments  which  dissolve  the 
substance  of  their  walls,  and  feed  on  the  products  of 
solution.  Hence  they  damage  the  timber  in  two  ways 
— they  riddle  it  through  and  through  by  myriads  of 
minute  apertures,  and  thus  ruin  its  structure,  and  they 


FIG.  42. — Piece  of  oak  destroyed  by   T"h(l<j<li",-«   /'-/•<//./•.  sliowinir  the 
characteristic  markings  due  to  the  action  of  the  fungus.    (R.  Ilartig.) 

reduce  its  substance  by  dissolving  it  and  converting  it  to 
their  own  uses.  The  wood,  therefore,  loses  in  strength 
and  in  weight,  and  becomes  "  rotten."  There  are  differ- 
ences in  detail  as  to  the  mode  of  destroying  the  elements 
of  the  wood,  but  the  final  result  is  much  the  same  in  all 


THE  CULTIVATION  OF  THE  OAK.  159 

cases  :  some  of  the  fungi  destroy  the  vessels,  fibers,  etc., 
by  dissolving  their  walls  from  inside,  while  others  de- 
stroy the  part  common  to  contiguous  cells,  etc.,  and 
thus  first  isolate  the  elements  and  then  complete  the 
destruction.  A  series  of  very  interesting  researches  by 


FIG.  43. — Oak  timber  destroyed  by  the  fungus  Hydnum  Jirersidens: 
a  shows  the  medullary  rays  on  the  tangential  section ;  b,  a  mass  of 
felted  mycelium.  (R.  Hartig.) 

Hartig  has  demonstrated  that  the  presence  of  these  tim- 
ber-destroying fungi  can  be  detected  from  the  markings 
and  discolorations  they  produce  in  the  wood  ;  those  due 
to  Hydnum  diversidens,  Thelepliora  Perdix,  Polyporus 
sulplmreus,  P.  igniarius,  P.  dryadeus,  and  Stereum 


160  THE   OAK. 


Mrsutum  being  all  different,  and  in  some  cases  so  char- 
acteristic that  the  merest  glance  suffices  to  diagnose  the 
disease  (cf.  Figs.  42  to  45). 

There  is  yet  another  disease  of  oak  timber  to  be 
noticed,  and  one  which  causes  great  havoc  in  buildings 


FIG.  44. — Oak  damaged  by  Polyporus  igniarius,  a  very  common  timber 
fungus.    (E.  Hartig.) 

where  the  ventilation  is  bad  and  the  air  damp.  This  is 
the  too  well  known  dry-rot,  due  to  the  destructive  action 
of  the  fungus  Merulius  lacrymans,  a  hymenomycete 
allied  to  the  preceding,  but  differing  from  them  in  not 
attacking  the  standing  timber.  The  spores  of  this 


THE   CULTIVATION   OF   THE   OAK. 


161 


fungus  are  able  to  infect  oak  planks,  beams,  etc. ;  and 
the  mycelium  rapidly  spreads  on  and  in  the  wood,  de- 
stroying the  cell-walls,  and  causing  the  wood  to  shrink 
and  crack  and  warp,  and  finally  to  fall  to  pieces.  Thor- 
ough ventilation  is  fatal  to  the  fungus  and  stops  the  rot. 


FIG.  45. — Oak  wood  destroyed  by  Polyporus  dryadeus,  showing  the  very 
characteristic  markings,  like  insect  tunnels  in  a  deep  red  brown  ma- 
trix. (K.  Hartig.) 

A  series  of  enemies  to  the  oak-tree  not  yet  referred 
to  are  various  gall-insects,  so  called  because  they  pierce 
the  young  leaves  or  buds,  etc.,  and  lay  their  eggs  in  the 
wound ;  the  irritation  set  up  suffices  to  induce  a  flow  of 
food  materials  to  the  stimulated  spot,  and  the  overfed 


FIG.  46. — Piece  of  oak-bark  with  fructification  of  Polyporus  sulphure'us. 


FIG.  47.— Piece  of  oak  attacked  by  Poly-pom  x  x/i //,/,,//•<•  UK,  th  e  yellowish 
white  mycelium  of  which  is  seen  at  c  and  d.    (K.  Hartig.) 


J 


FIG.  48. — Transverse  section  of  oak-timber  destroyed  by  Polyporus  sul- 
phureus.     (E.  Ilartig.) 


FIG.  49. — Highly  magnified  longitudinal  radial  section  of  a  piece  of  oak 
destroyed  by  a  timber  fungus,  showing  the  ravages  of  the  hyphse  in 
the  various  tissues.  (K.  Hartig.) 


164:  THE   OAK. 

cells  multiply  and  form  the  gall.  This  is  a  mere  out- 
line sketch  of  the  matter,  however,  for  the  differences  in 
behavior  are  enormous.  Each  insect  causes  the  forma- 


FIG.  50.— Portion  of  the  spore-bearing  hymenium  of  Merulim  lacrymans, 
the  fungus  of  "  dry  rot." 

tion  of  a  specific  kind  of  gall,  differing  in  shape,  size, 
color,  and  other  characters  from  those  caused  by  other 
gall-insects.  There  are  many  kinds,  and  only  a  few  can 
be  mentioned  here.  Each  species  of  oak  may  have  its 


THE   CULTIVATION   OF  THE   OAK. 


165 


own  galls  also,  those  on  the  American  oaks  differing 
from  those  on  the  European  species,  but  some  are  com- 
mon to  more  than  one  species.  The  insects  which  pro- 


FIG.  51. — An  oak-leaf  with  several  kinds  of  Cynips  galls  on  it:  a,  gall 
produced  by  Cynips  seutellaris  ;  J,  C.  divisa ;  c,  Neuroterus  Reau- 
murii;  e,  BiorJiisa  renum;  f,  Neuroterus  ostreus.  (Frank.) 

duce  the  commonest  English  oak-galls  are  nearly  all 
members  of  the  Cynipidece,  a  group  of  hymenoptera 
which  lay  their  eggs  in  the  young  tissues  of  various 

plants,  especially  oaks  and  roses. 
12 


166  THE  OAK. 

Some  of  the  resulting  galls  are  discoid,  such  as  the 
"  oak-spangles  "  of  our  woods ;  others,  again,  are  spheri- 
cal, such  as  the  common  leaf -galls  so  well  known  in  Eng- 
land, and  the  so-called  oak-apple;  then  there  are  the 
"artichoke  galls,"  produced  by  the  partial  metamor- 
phosis of  the  buds  of  the  oak  in  which  the  Cynips  has 
laid  its  egg,  and  many  others. 


CHAPTER  XII. 

RELATIONSHIPS    OP    THE    OAKS — THEIR    DISTRIBUTION" 
IN    SPACE    AND    TIME. 

THE  oak  is  a  member  of  a  very  large  and  ancient 
group  of  dicotyledonous  flowering  plants,  embracing  the 
beeches,  chestnuts,  hazel-nuts,  etc.,  and  many  other 
forest  trees  of  the  Northern  Hemisphere. 

The  number  of  species  of  oaks  ( Quercus)  is  very  large, 
probably  more  than  300,  of  which  the  majority  belong 
to  North  America,  Europe,  China,  Japan,  and  other 
parts  of  Asia.  There  are  none  in  Africa  south  of  the 
Mediterranean  region,  nor  in  South  America  orA  ustral- 
asia.  Some  remarkable  species  are  found  in  the  Hima- 
layas, and  many  in  the  Malayan  Archipelago. 

The  various  species  of  the  genus  Quercus  are  ar- 
ranged into  groups  according  to  differences  in  the  form 
and  arrangement  of  the  scales  of  the  cupule,  the  charac- 
ters of  the  leaves,  and  certain  peculiarities  in  the  acorns. 
Many  oaks,  especially  those  of  warm  countries,  for  in. 
stance,  are  "  evergreen,"  with  hard,  leathery  leaves,  quite 
unlike  the  leaves  of  our  common  British  oak. 

The  latter  is  denominated  botanically  as   Quercus 


168  THE   OAK. 

Robur,  but  certain  varietal  forms  of  it  have  been  distin- 
guished, of  which  the  commonest  in  this  country  are  Q. 
pedunculata^  a  variety  with  the  female  flowers  on  long 
peduncles,  and  Q.  sessiliflora,  with  the  female  flowers  on 
short  peduncles ;  but  although  numerous  attempts  have 
been  made  to  define  these  forms,  and  while  small  differ- 
ences in  the  petioles,  lobing  of  the  leaves,  and  the  wood, 
etc.,  have  been  insisted  upon  at  various  times  by  ob- 
servers, it  appears  that  the  two  varieties  graduate  into 
one  another  by  intermediate  forms.  In  England,  the 
variety  pedunculata  is  the  commonest  over  the  country 
generally,  but  in  the  hilly  districts  of  North  "Wales  and 
the  north  of  England  the  variety  sessiliflora  is  said  to 
prevail.  Similarly,  on  the  Continent  the  latter  variety 
is  found  at  higher  elevations  than  the  former,  though  its 
area  of  occurrence  is  more  restricted.  This  pronounced 
variability  of  the  oak  was  commented  upon  by  the  late 
Charles  Darwin,  who  points  out,  in  the  Origin  of  Species, 
that  more  than  a  dozen  species  have  been  made  by  a 
certain  author  out  of  what  other  botanists  regard  as 
mere  varieties  of  the  common  oak. 

De  Candolle,  who  made  a  special  study  of  this  group, 
found  the  variations  so  enormous  that,  although  he 
made  something  like  300  species,  he  decided  that  the  ma- 
jority of  these  were  merely  provisional ;  and  he  conclud- 
ed, as  others  have  done,  that  we  have,  in  the  numerous 
varieties  of  the  species  of  this  old  genus  Quercus,  series 
of  incipient  species.  If  the  connecting  forms  were  to 
die  out,  leaving  certain  varieties  more  isolated  than  they 


RELATIONSHIPS  OF  THE  OAKS.  169 

are  at  present,  systematists  would  elevate  the  latter  to 
the  rank  of  species. 

It  is  interesting  to  observe  that  twenty-eight  varie- 
ties of  the  common  English  oak  (Q.  Robur)  have  been 
described,  and  that  the  majority  of  these  can  be  grouped 
around  the  three  forms  pedunculata,  sessiliflora,  and 
pubescenS)  the  latter  being  a  somewhat  hairy  variety 
found  on  the  Continent.  No  doubt  we  have  here,  again, 
a  case  where  the  three  varieties  mentioned  would  be 
accorded  specific  rank  if  the  connecting  forms  died  out, 
as  some  of  them  appear  to  be  doing. 

I  have  already  stated  that  the  oaks  are  a  very  ancient 
family,  and  their  great  variability  is  in  accordance  with 
this.  It  probably  implies  that  the  genus  has  had  time 
during  its  migrations  over  the  Northern  Hemisphere  to 
vary  immensely,  and  that  some  of  the  varieties  have  be- 
come adapted  to  given  situations,  others  to  others.  On 
the  whole,  the  oak  family  must  be  regarded  as  a  north- 
ern type  which  has  sent  extensions  southward. 

Now  let  us  glance  at  their  geological  history.  Some- 
thing like  200  forms  of  fossil  oaks  have  been  described 
from  remains,  chiefly  of  leaves  and  wood,  found  in  vari- 
ous parts  of  the  world.  Some  of  the  European  fossil 
forms  remind  us  of  species  now  found  only  in  hot  coun- 
tries near  the  tropics,  others  are  peculiar,  and  some  are 
very  doubtful. 

The  earliest  remains  of  oaks  come  from  the  Creta- 
ceous strata,  being  coeval  with  the  first  undoubted  dico- 
tyledons that  have  been  found.  Many  have  been  found 


170  THE   OAK. 

in  the  Tertiary  also,  and  we  have  to  conclude  that  the 
oaks  were  probably  already  a  well-developed  group  of 
plants  before  the  higher  mammalia  existed — i.  e.,  so  far 
as  we  can  judge  from  the  fragmentary  records  of  the 
rocks.  It  seems  that  even  the  present  species  of  oaks 
were  already  in  existence  in  Tertiary  times,  and  possibly 
some  of  their  varieties  also. 

From  the  evidence  of  their  fossil  remains,  together 
with  the  facts  of  their  present  distribution,  it  is  at  least 
exceedingly  probable  that  the  European  oaks,  including 
our  English  oak,  came  into  existence  somewhere  in  the 
East,  and  that,  after  spreading  from  Asia  towards  the 
West,  they  are  now  slowly  retreating  before  competing 
forms — e.  g.,  the  beech.  Meanwhile  the  English  oak 
(Q.  Robur)  has  been  giving  rise  to  several  varieties,  of 
which  three  at  least  (viz.,  pedunculata,  sessiliflora,  and 
pubescens)  have  become  sufficiently  marked  to  be  re- 
garded as  species  by  those  who  do  not  consider  the  con- 
necting forms. 

It  is  not  improbable  that  this  migration  of  the  Euro- 
pean oaks  from  Asia  was  completed  before  the  islands 
of  Sicily,  Sardinia,  Corsica,  and  Britain  were  separated 
from  the  mainland  of  the  Continent.  Moreover,  our 
English  oak  is  not  distantly  related  to  certain  species 
of  Eastern  Asia  and  of  Western  North  America,  and  it 
has  been  surmised  that  all  these  related  forms  sprang 
from  a  common  ancestor  not  unlike  our  English  oak 
of  to-day.  Again,  fossil  leaves  from  Italy,  found  in 
diluvial  deposits,  are  so  like  those  of  certain  Californian 


RELATIONSHIPS  OF  THE  OAKS.  171 

oaks  now  existing  that  a  common  origin  is  also  sug- 
gested, and  similar  leaves  have  been  discovered  in  Ter- 
tiary deposits  in  Northwest  America.  If  all  the  evi- 
dence is  put  together,  we  may  conclude  with  Asa  Gray 
that  "  the  probable  genealogy  of  Q.  Robur,  traceable  in 
Europe  up  to  the  commencement  of  the  present  epoch, 
looks  eastward  and  far  into  the  past  on  far-distant 
shores." 

Many  of  the  oaks  yield  products  which  are  made  use 
of  in  the  arts,  apart  from  their  timber,  the  most  valu- 
able of  which  comes  from  our  European  oak,  the  white 
oaks  of  North  America,  and  one  or  two  Himalayan 
species.  In  several  countries  oaks  are  grown  for  the 
sake  of  the  bark,  cups,  etc.,  as  a  tanning  material,  and 
these  even  form  important  articles  of  export.  Quer- 
citron, a  yellow  dye  and  tanning  material,  is  obtained 
from  Q.  tinctoria  in  North  America. 

Cork,  as  used  for  bottling  and  other  purposes,  is 
obtained  in  Spain,  the  south  of  France,  and  in  Algiers, 
from  the  thick  periderm  of  Q.  Siiber. 

Q.  infectoria  yields  the  chief  galls  of  commerce. 
They  are  caused  by  the  punctures  of  Cynips  gallw  tinc- 
torice,  and  are  used  for  making  ink  and  for  dyeing.  In 
these  and  similar  galls  the  value  depends  on  the  pres- 
ence of  relatively  large  quantities  of  tannic  and  gallic 
acids  which  they  contain. 


INDEX. 


Accessory  shoots,  6. 
Acorn,  4,  7,  10-23, 130  ;  figs.  1-3. 
Age  of  oak,  J51. 
Alburnum,  110,  136. 
Annual  rings,  95-108,  136. 
Axis-cylinder,    24,     28,    32,    91; 
fig.  5. 

Bark,  98,  111,  118-120;  fig.  30. 

Bast.     See  Phloem. 

Beech,  148,  151. 

Biology  of  roots,  36. 

Bud,  50,  72-76,  127;  figs.  19,  32. 

Burning  of  oak,  142. 

Burrs,  7. 

Cambium,  40,  52,  64,  92,  98,  100, 

103,  111 ;  figs.  9,  24. 
Cattle,  155. 
Cells,  15,  136. 
Chlorophyll,  79,  85. 
Cnethocampa,  1 54. 
Common  bundles,  47. 
Coppice,  149. 

Cork,  93,  116;  figs.  17,  18. 
Cortex,  52,  98;  figs.  17,  18. 
Cotyledons,  14,  130,  134 ;  figs.  2, 

3,  37. 
Course  of  vascular  bundles,  42-51, 

68-71 ;  figs.  10,  11. 
Cultivation  of  oak,  147-152. 
Cupule,  10,  124,  130. 
Cynipe,  153,  162;  fig.  48. 


Density  of  oak,  138. 
Diseases  of  oak,  152-163. 
Drainage,  153. 
Dry-rot.     See  Merulius. 
Durability  of  oak,  142. 
Duramen,  109,  136. 

Elasticity  of  oak,  140. 

Embryo,  14. 

Embryonic  tissue,  17,  28,  41,  96; 

figs.  2,  6,  25. 
Embryo-sac,  128  ;  fig.  35. 
Endodermis,  30,  32 ;  fig.  5. 
Epidermis,  16,  39,  41,  52. 

Fertilization,  130. 

Fibers,  60,    106,    108,    113,  136; 

fig.  16. 

Flexibility  of  oak,  141. 
Flowers  of  oak,  121 ;  figs.  31,  32. 
Folk-lore,  2,  3. 
Fruit  of  oak,  10,  131. 
Fundamental  tissue,  16,  39. 
Fungi,  96,  153,  156-163  ;  figs.  25, 

42-47. 

Gall-insects,  161 ;  fig.  48. 
General  description  of  oak,  5. 
Germination,  10-23. 
Growing-point,  37,  74,  96  ;  figs.  6, 

19. 
Growth  in  thickness,  68,  91,  100- 

103. 


INDEX. 


Habit  of  oak,  150. 

Hardness  of  oak,  141. 

Heart-wood.     See  Duramen. 

High  forest,  147. 

Honeysuckle,  155. 

Hornbeam,  148. 

Hydnum  diversidens,  159  ;  fig.  43. 

Hymenomycetes,  157. 

Hyphse,  97,  157  ;  fig.  25. 

Hypocotyl,  fig.  3. 

Inflorescence  of  oak,  121 ;  figs.  31, 
32. 

Injuries  to  which  the  oak  is  sub- 
ject, 152-163. 

Insects,  154. 

Lammas  shoots,  6,  74. 

Leaf,  21,  76-88;  figs.  20,  21,  22. 

Leaf-trace,  47,  49,  69. 

Lenticels,  1 14. 

Loranlhus  europ&us,  155  ;  fig.  41. 

Medullary  rays,  34,  39,  48,  52,  54, 
63,  95,  100,  104,  136;  figs.  9, 
12,  27,  38. 

Mertilius  lacrymans,  160  ;  figs.  46, 
47. 

Mesophyll,  76,  79,  81,  85  ;  fig.  22. 

Mistletoe,  155. 

Mixed  woods,  148. 

Mycorhiza,  96 ;  figs.  7,  25. 

Nectria,  156. 

Oak-apple,  163. 
Oak-moth.     See  Tortrix. 
Ovary,  124,  130;  figs.  33,  34. 
Overcrowding,  153. 
Ovules,  125,  128;  figs.  34,  35. 

Parenchyma,  18. 


Peculiarities  of  oak,  142. 
Pericarp,  12,  131  ;  figs.  2,  3,  37. 
Pericycle,  30,  32 ;  fig.  5. 
Periderm,  93,  111,  117. 
Perigone,  124. 
Phellem.     See  Cork. 
Pbelloderm,  117. 
Phellogen,  116. 
Phloem,    32,    40,    52-71,    92,   99, 

103,   111;  figs.  5,  6,  9,  17,  18, 

24. 

Phyllactinia,  156. 
Phyllotaxis,  42,  47,  78,  122. 
Physiology  of  roots,  35. 

of  leaf,  83-87,  91. 

of  stem,  90. 

Piliferous  layer,  24,   32,  91 ;  figs. 

5,  6. 
Pith,  39,  52,  55,  98,  136 ;  figs.  5, 

12,  99. 

Plasticity  of  roots,  35. 
Plumule,  14,  21,  130;  figs.  2,  3. 
Pollen,  123,  128. 
Pollination,  123,  126. 
Polyporus  dryadeus,  159  ;  fig.  45. 

igniariw,  159  ;  fig.  44. 

sulphureus,  159. 

Primary  root,  14,  22 ;  fig.  3. 
Primary  shoot,  21,  39  ;  fig.  4. 
Procambium,  42. 
Properties  of  oak,  136-146. 
Proteids,  17,  18. 
Protoplasm,  17. 
Pure  oak  woods,  147. 

Qualities  of  oak,  144  ;  fig.  39. 
Quercite,  18. 
Qiiercuspedunculata,  7,  123,  138. 

Robur,  7,  8. 

se&siliflora,  7,  76,  138. 


INDEX. 


175 


Radicle,  14,  130;  figs.  2,3. 

Structure  of  oak,  136. 

Requirements  of  oak,  149. 

of  root,  24  ;  fig.  5. 

Rocking  of  root,  20,  35. 

Swelling  of  oak,  140.  . 

Root-cap,  23,  25,  32  ;  fig.  6. 

Root-cortex,  24,  28,  32,  91  ;  figs. 

Tannin,  9,  17,  68,  135. 

5,6. 

Technology  of  oak,  136-146. 

Root-hairs,  23,    28,    36,    82,   97; 

Tenacity  of  oak,  140. 

fig.  3. 

Testa,  13,  131  ;  figs.  2,  3. 

Root-system,  38,  91-97. 

Thelcphora  Perdiz,  159  ;  fig.  42. 

Jtosellinia,  153. 

Timber,  8,  136-146  ;  figs.   26,  38, 

39. 

Sapling,  4,  89. 

Tissues,  17,  39. 

Sap  wood.     See  Alburnum. 

Torsion  of  oak,  141. 

Scale-leaves,  21. 

Tortrix  viridana,  154  ;  fig.  40. 

Secondary  roots,  34  ;  fig.  3. 

Tracheids,  60,  106,  108,  136  ;  fig. 

Seed  of  oak,  10,  12,  132  ;  figs.  36, 

16. 

37. 

Tree-killing  fungi,  157. 

Seed-coat.     See  Testa. 

Tyloses,  110;  fig.  29. 

Seed-leaves.     See  Cotyledons. 

Seed-trees,  149,  151. 

Uses  of  oak,  143. 

Seedling,  4,  19-24,89;  fig.  3. 

Sheath,  fig.  5. 

Vascular  bundles,  11,  17,  18,  26, 

Shoot-axis,  22,  39,  75,  98  ;  figs.  9, 

41-51,  100  ;  figs,  2,  3,  9,  10-12. 

26. 

system,  51-71. 

Shoot-system,  6,  39,  98-120. 

Venation  of  leaf,  49,  70,  76,  79  ; 

Shrinkage  of  oak,  139. 

fig.  21. 

Sieve-tubes,  32,  112. 

Vessels,  30,  31,  40,  55-62,  90,  106, 

Silver  fir,  148. 

108,  136  ;  figs.  12-16,  38. 

Splitting  of  oak,  141. 

Spruce,  148. 

Stamen,  123. 

Water  in  oak,  139. 

Starch  -grains,  17,  18,  87. 
Stereum  hirsutum,  159. 

Winter  state,  7. 
Wood.     See  Xylem. 

Stigma,  12,  123. 

Wood-cells,  31,  62,  106  ;  fig.  16. 

Stipules,  22,  74,  122,  127;  figs.  4, 

19,  32. 

Xylem,    30,   40,   52-71,    92,   100, 

Stomata,  82  ;  fig.  23. 

103,  111  ;  figs.   5,  6,  9,  13-15, 

Stores  of  food  materials,  20,  88. 

24. 

D.  APPLETON  &  CO. '8  PUBLICATIONS. 


SIR  JOHN    LUBBOCK'S  (Bart.)  WORKS. 

THE  ORIGIN  OF  CIVILIZATION  AND  THE  PRIMI« 
TIVE  CONDITION  OF  MAN,  MENTAL  AND  SOCIAL 
CONDITION  OF  SAVAGES.  Fourth  edition,  with  numerous  Ad- 
ditions,  With  Illustrations.  8vo.  Cloth,  $5.00. 

"  This  interesting  work— for  it  is  intensely  so  in  its  aim,  scope,  and  the  abil- 
ity of  its  author— treats  of  what  the  scientists  denominate  anthropology,  or  the 
natural  history  of  the  human  species  ;  the  complete  science  of  man,  body,  and 
soul,  including  sex,  temperament,  race,  civilization,  etc."— Providence  Press. 

PREHISTORIC  TIMES,  AS  ILLUSTRATED  BY  ANCIENT 
REMAINS  AND  THE  MANNERS  AND  CUSTOMS  OF  MODERN 
SAVAGES.  Illustrated.  8vo.  Cloth,  $5.00. 

"This  is,  perhaps,  the  best  summary  of  evidence  now  in  onr  possession  con- 
cerning the  general  character  of  prehisto  ric  times.  The  Bronze  Age,  The  Stone 
Age,  The  Tumuli.  The  Lake  Inhabitants  of  Switzerland,  The  Shell  Mounds,  The 
Cave  Man,  and  The  Antiquity  of  Man,  are  the  titles  of  the  most  important  chap- 
ters."—Dr.  C.  K.  Adams's  Manual  of  Historical  Literature. 

ANTS,  BEES,  AND  WASPS.  A  Record  of  Observations  on  the 
Habits  of  the  Social  Hymenoptera.  With  Colored  Plates.  12mo. 
Cloth,  $2.00. 

"This  volume  contains  the  record  of  various  experiments  made  with  ants, 
bees,  and  wasps  during  the  last  ten  years,  with  a  view  to  test  their  mental  con- 
dition and  powers  of  sense.  The  author  has  carefully  watched  and  marked  par- 
ticular insects,  and  has  had  their  nests  under  observation  for  long  periods— one 
of  his  ants'  nests  having  been  under  constant  inspection  ever  since  1874.  His 
observations  are  made  principally  upon  ants,  because  they  show  more  power  and 
flexibility  of  mind  ;  and  the  value  of  his  studies  is  that  they  belong  to  the  de- 
partment of  original  research." 

ON    THE    SENSES,    INSTINCTS,    AND    INTELLIGENCE 

OF  ANIMALS,  WITH  SPECIAL  REFERENCE  TO  INSECTS. 

"  International  Scientific  Series."     With  over  One  Hundred  Illustra- 
tions.    12mo.     Cloth,  $1.75. 

The  author  has  here  collected  some  of  his  recent  observations  on  the  senses 
and  intelligence  of  animals,  and  especially  of  insects,  and  has  attempted  to  give, 
very  briefly,  some  idea  of  the  organs  of  sense,  commencing  in  each  case  with 
those  of  man  himself. 

THE  PLEASURES  OF  LIFE.  12mo.  Cloth,  50  cents ;  paper, 
25  cents. 

CONTENTS.— THE  DUTY  OF  HAPPINESS.  THE  HAPPINESS  OF  DUTY.  A 
SONG  OF  BOOKS.  THE  CHOICE  OF  BOOK?.  THE  BLESSING  OF  FRIENDS.  THE 
VALUE  OF  TIME.  THE  PLEASURES  OF  TRAVEL.  THE  PLEASURES  OF  HOME. 
SCIENCE.  EDUCATION. 


New  York :  D.  APPLETON  &  CO.,  1,  3,  &  5  Bond  Street. 


D.  APPLETON  &  CO.'S  PUBLICATIONS. 


JOHN    TYNDALL'S   WORKS. 

ESSAYS  ON  THE  FLOATING   MATTER  OF   THE  AIR, 

in  Relation  to  Putrefaction  and  Infection.     12mo.     Cloth,  $1.50. 

ON  FORMS  OF  WATER,  in  Clouds,  Rivers,  Ice,  and  Glaciers. 
With  35  Illustrations.  12tno.  Cloth,  $1.50. 

HEAT  AS  A  MODE  OF  MOTION.  New  edition.  12mo. 
Cloth,  $2.50. 

ON  SOUND :  A  Course  of  Eight  Lectures  delivered  at  the  Royal 
Institution  of  Great  Britain.  Illustrated.  12mo.  New  edition. 
Cloth,  $2.00. 

FRAGMENTS  OF  SCIENCE  FOR  UNSCIENTIFIC  PEO- 
PLE. 12mo.  New  revised  and  enlarged  edition.  Cloth,  $2.50. 

LIGHT  AND  ELECTRICITY.     12mo.     Cloth,  $1.25. 
LESSONS    IN    ELECTRICITY,  1875-"76.     12mo.    Cloth,  $1.00. 

HOURS  OF  EXERCISE  IN  THE  ALPS.  With  Illustrations. 
12mo.  Cloth,  $2.00. 

FARADAY  AS  A  DISCOVERER.  A  Memoir.  12mo.  Cloth, 
$1.00. 

CONTRIBUTIONS  TO  MOLECULAR  PHYSICS  in  the  Do- 
main of  Radiant  Heat.  $5.00. 

SIX  LECTURES  ON  LIGHT.  Delivered  in  America  in  1872- 
'73.  With  an  Appendix  and  numerous  Illustrations.  Cloth,  $1.50. 

FAREWELL  BANQUET  given  at  Delmonico's,  New  York.  Paper, 
50  cents. 

ADDRESS  delivered  before  the  British  Association,  assembled  at  Bel- 
fast. Revised,  with  Additions.  12mo.  Paper,  50  cents. 

RESEARCHES  ON  DIAMAGNETISM  AND  MAGNE- 
CRYSTALLIC  ACTION,  including  the  Question  of  Diamag- 
netic  Polarity.  With  Ten  Plates.  12mo.  Cloth,  $1.50. 

NEW  FRAGMENTS.     12mo.     Cloth,  $2.00. 

New  York :  D.  APPLETON  &  CO.,  1,  3,  &  6  Bond  Street. 


D.  APPLETON  &  CO.'S  PUBLICATIONS. 

THOMAS  H.   HUXLEY'S  WORKS. 

SCIENCE  AND  CULTURE,  AND  OTHER  ESSAYS.  12mo. 
Cloth,  $1.50. 

THE  CRAYFISH:  AN  INTRODUCTION  TO  THE  STUDY 
OF  ZOOLOGY.  With  82  Illustrations.  12mo.  Cloth,  $1.75. 

MAN'S   PLACE   IN   NATURE.     12mo.     Cloth,  $1.25. 
ON  THE  ORIGIN  OF  SPECIES.     12mo.     Cloth,  $1.00. 

MORE  CRITICISMS  ON  DARWIN,  AND  ADMINISTRATIVE 

NIHILISM.     12mo.     Limp  cloth,  50  cents. 

MANUAL  OF  THE  ANATOMY  OF  VERTEBRATED 
ANIMALS.  Illustrated.  12mo.  Cloth,  $2.50. 

MANUAL   OF  THE  ANATOMY   OF   INVERTEBRATED 

ANIMALS.     12mo.     Cloth,  $2.50. 

LAY   SERMONS,   ADDRESSES,   AND    REVIEWS.     12mo. 

Cloth,  $1.75. 

CRITIQUES  AND  ADDRESSES.     12mo.     Cloth,  $1.50. 

AMERICAN  ADDRESSES;  WITH  A  LECTURE  ON  THE 

STUDY  OF  BIOLOGY.     12mo.     Cloth,  $1.25. 

PHYSIOGRAPHY  :  AN  INTRODUCTION  TO  THE  STUDY  OF 
NATURE.  With  Illustrations  and  Colored  Plates.  12mo.  Cloth, 
$2.50. 

THE  ADVANCE  OF  SCIENCE  IN  THE  LAST  HALF. 
CENTURY.  12mo.  Paper,  25  cents. 


New  York:    D.  APPLETON  &  CO.,  1,  3,  &  5  Bond  Street. 


T 


T1 


D.  APPLETON  &  CO.'S  PUBLICATIONS. 

rjrffE  ICE  AGE  IN  NORTH  AMERICA,  and  its 

J-  Bearings  ^^pon  the  Antiquity  of  Man.  By  G.  FREDERICK 
WRIGHT,  D.  D.,  LL.  D.  With  152  Maps  and  Illustrations. 
Third  edition,  containing  Appendix  on  the  "  Probable  Cause  of 
Glaciation,"  by  WARREN  UPHAM,  F.  G.  S.  A.,  and  Supplement- 
ary Notes.  8vo.  625  pages,  and  complete  Index.  Cloth,  $5.00. 

"Prof.  Wright's  work  is  great  enough  to  be  called  monumental.  There  is  not 
a  page  that  is  not  instructive  and  suggestive.  It  is  sure  to  make  a  reputation  abroad 
as  well  as  at  home  for  its  distinguished  author,  as  one  of  the  most  active  and  intelligent 
of  the  living  students  of  natural  science  and  the  special  department  of  glacial  action." 
—Philadelphia  Bulletin. 

E  GREAT  ICE  AGE,  and  its  Relation  to  the 
Antiquity  of  Man.  By  JAMES  GEIKIE,  F.  R.  S.  E.,  of  H.  M. 
Geological  Survey  of  Scotland.  With  Maps  and  Illustrations. 
I2mo.  Cloth,  $2.50. 

A  systematic  account  of  the  Glacial  epoch  in  England  and  Scotland,  with  special 
reference  to  its  changes  of  climate. 

E  CAUSE  OF  AN  ICE  AGE.  By  Sir  ROBERT 
BALL,  LL.  D.,  F.  R.  S.,  Royal  Astronomer  of  Ireland,  author  of 
"Starland."  The  first  volume  in  the  MODERN  SCIENCE  SE- 
RIES, edited  by  Sir  JOHN  LUBBOCK.  I2mo.  Cloth,  $1.00. 

"An  exceedingly  bright  and  interesting  discussion  of  some  of  the  marvelous  phys- 
ical revolutions  of  whicli  our  earth  has  been  the  scene.  Of  the  various  ages  traced  and 
located  by  scientists,  none  is  more  interesting  or  can  be  more  so  than  the  Ice  age,  and 
never  have  its  phenomena  been  more  clearly  and  graphically  described,  or  its  causes 
more  definitely  located,  than  in  this  thrillingly  interesting  volume." — Hasten  Traveller. 

'TO  WN  GEOLOG  Y.   By  the  Rev.  CHARLES  KINGSLEY, 
•1        F.  L.  S.,  F.  G.  S.,  Canon  of  Chester.    I2mo.     Cloth,  $1.50. 

"  I  have  tried  rather  to  teach  the  method  of  geology  than  its  facts:  to  furnish  the 
student  with  a  key  to  all  geology ;  rough  indeed  and  rudimentary,  but  sure  and  sound 
enough,  1  trust,  to  help  him  to  unlock  most  geological  problems  which  may  meet  him 
in  any  quarter  of  the  globe." — Prom  the  Preface. 

/IN   AMERICAN    GEOLOGICAL    RAIL  WAY 
*1     GUIDE.     Giving  the  Geological  Formation  along  the  Rail- 
roads, with  Altitude  above  Tide-water,  Notes  on  Interesting 
Places  on  the  Routes,  and  a  Description  of  each  of  the  Forma- 
tions.   By  JAMES  MACFARLANE,  Ph.  D.,  and  more  than  Seventy- 
five  Geologists.     Second  edition,  426  pp.,  8vo.     Cloth,  $2.50. 
"  The  idea  is  an  original  one.  .  .  .  Mr.  Macfarlane  has  produced  a  very  convenient 
a«d  serviceable  hand-book,  available  alike  to  the  practical  geologist,  to  the  student  of 
that  science,  and  to  the  intelligent  traveler  who  would  like  to  know  the  country  through 
which  he  is  passing." — Boston  Evening  Transcript. 

New  York :  D.  APPLETON  &  CO.,  i,  3,  &  5  Bond  Street. 


University  of  California 

SOUTHERN  REGIONAL  LIBRARY  FACILITY 

405  Hilgard  Avenue,  Los  Angeles,  CA  90024-1388 

Return  this  material  to  the  library 

from  which  it  was  borrowed. 


MAR  18  199- 


Form  L9-Serie8  444 


SOUTHERN  REGIONAL  LIBRARY  FACILITY 


001  105  564    7 


